Boring (This is a +1 sword) [voted=yes]
I dislike the idea of boring magical items. Magic items should be something wondrous, something to be held in awe, fear, or some other notable emotion. It should not be "ho, hum, oh? another magic item? okay." It doesn't necessarily have to have much to make it a bit more interesting - just something to make it stand out a bit, excite a bit of interest, suggest new unusual uses, and so forth is enough. Perhaps that magic sword hums, granting a +1 to bards using bardic music. Perhaps that spear can turn undead once per day as a second level cleric. Perhaps the bow alters the clothing of the wielder while the string is drawn, such that they gain +4 to Hide checks. Just little things that might perhaps be useful and certainly add more interest to the backstory of the item is nice.
Weak (It only gives a +1 bonus) [voted=no]
Weakness is never much of an issue with magic weapons. By their very nature they are above and beyond non-magical items. Anything beyond this relates to "Need," below.
Powerful (It ignores DR/magic completely) [voted=no]
Magic items, while being more powerful than normal items, should not be so powerful as to potentially break the game. If the weapon defeats any foe with ease, if the armor stops any injury, then the game becomes little more than a hack n slash computer-esque game without any substance. There is no longer any risk, any excitement, for the final result is a foregone conclusion due to the over-the-top magic item(s) of the player. This is almost as bad as a DM(N)PC that steals the show.
Despite these reasons, in the end I voted 'no'. It is a classic motiff in fantasy myths and literature that magic items are rare and potent. So long as this is true - and so long as they are not 'one shot, one kill' or 'perfect weapon against any/all foes' then there is not necessarily a problem. True, the fighter may be able to dispatch any troll or ogre with casual ease, but if his weapon is little better than a masterwork against all other creatures, it is not too unbalancing for the game. Also, if it is a question of the magic items being so powerful because the foes they fight cannot be defeated without such weapons, then again it becomes a question of 'Need' rather than just a question of 'Power'.
And while this may trod upon the steps of 'Entitlement', I do not mind PCs each having a powerful magic item or two - they are the rare and daring heroes of legend, after all. So long as magic items that powerful are rare and are not 'be all, end all, solves every problem', I generally have no problem with (some) magic items being quite potent.
Common (Every NPC has a +1 sword) [voted=yes]
This is a major problem. Magic items should be rare. They should not be on default treasure lists or on lists of standard equipment. Indeed, one of the differences between (nearly all) NPCs and PCs should be access to magical items. Few NPCs should have such access. I would even go so far as to state that NPC classes are not necessary, so long as only PCs have access to magical weapons and armor. Two fighters of similar level - if one has +x armor and +x weapons, while the other has mere masterwork, would there be any question as to which was the more potent? There is no need to further minimize an NPC with a warrior class (which is no more than a fighter without feats). As most NPCs would be no more than a few levels anyway, the few differences would make little difference, but this is a matter for another post, so I will leave off here on this topic.
Glut (The PCs also have a +1 bow, +1 armor, +1 shield, +1 ring, +1 cloak, +1 amulet ...) [voted=yes]
This is a problem. I can see masterwork for most of their items, for they are rare and celebrated heroes, who have done major deeds and been appropriately awarded (with either the masterwork items or with wealth or contacts that latter provided masterwork items, etc). However, magic should be rare or at least uncommon. Magic should not be necessary, and while a bit of entitlement is understandable and even expected, it should not range to such petty 'complete the set' mentalities. These are not collectible cards, after all.
In a sense, this is only a problem because of several other problems. It only shows up when magic items are common and when the PCs actually need magic items to succeed. So long as magic items are not needed and are not common, magic glut should not be an issue.
Manufacture (The PCs can make a +1 sword) [voted=no]
I have never had an issue with PCs making magic items - so long as the resources required make it difficult enough that magic item rarity (or uncommonness) is maintained. If the PC needs a feather from a phoenix to make that fireburst sword, and phoenixes can only be found in the volcanic mountains found a month's journey to the west across hostile territory or difficult wilderness / frontier land, then why should it be a problem. Permanent items should be difficult to make. Potions are not much of an issue because they are increasingly less useful at higher levels (due to level limiting). Even without that, one time use items are a common motiff in fantasy - whether potion, or food, or arrow, or ring with a single spell trapped within it.
Wands and staves are troublesome, but due to the limits of the magic system they are somewhat understandable. I look forward to some of what I've heard about 4e, in fact, as it seems their nature and use will be changing.
Trade (The PCs can buy or sell a +1 sword) [voted=yes]
This is a problem of commonality. So long as magic items are common then it should be expected that they can be trades, sold, etc like any other common item. Rare items - as magic items should be - are like major works of art: their value is variable, subjective. They might be auctioned off for a price, but each time they are up for sale, the price they receive will differ, maybe higher this time, maybe lower next time. Also, some will look at the item and see little worth in it, while others are willing to sell their soul for it. Such an item cannot be truly bought or sold, for its value is always in flux, and its rarity makes collecting and selling such quite difficult in the first place, let alone as a common profession.
Need (The PCs must have +1 swords) [voted=yes]
Magic items should never be needed to succeed in a goal. They may make a goal easier to achieve, but never should success be impossible without one. PCs should at least have a chance of success on their own merits, even if they are reduced to only masterwork items or worse. Along with commonality, this is a major problem with magic items. Glut and Trade are mere symptoms of these.
Entitlement (The players expect to get +1 swords) [voted=no]
I don't mind PCs feeling entitled to magic items - so long as magic items are neither common nor taken for granted. They should expect their magic items to catch the eyes of every thief if they are willing to constantly show them off and speak of them. They should treat their items like the rare and valuable items they are, not like just another tool for the job. So long as they do not expect a glut of magic items or every magic item to be supremely powerful, then I have no problem with handing out a few items, with perhaps one being uncommonly powerful against a particular for or in a particular situation.