4 can be resolved using the fractional bab/save rules in UA (which also resolves the problem of 3/4 bab classes haemorraghing their bab inadvertantly unless they stopped at 4 lvs of each.
I am fine with 2 and 5 though. To me, it is more of something that DMs should adjudicate accordingly to the requirements of their game, rather than a limitation hard-coded into the game's mechanics. Multiclassing does not always produce broken characters, nor do you necessarily need to multiclass to obtain a powerful PC. Druid20 is the best example.
Some may be fine allowing a dip in barb for pounce, arguing that it is a small step towards keeping melees in line with spellcasters (and others less so). The best solution, IMO, would be to have the DM vet through everyone's build prior to running the game and ensure that everything is in order. If you are unhappy with his barb/fighter/bear warrior/warshaper/frenzied berserker build which you feel will upset game balance, then have it rebuild it. If you think the party can handle it, allow it by all means.
I don't think there is a clear 1-size-fits-all solution here, nor would one be desirable.
[sblock=Example
![Devious :] :]](http://www.enworld.org/forum/images/smilies/devious.png)
A long while back I went to the Character Optimization board with a build request, and I ended up with a character build with eight classes -- two base, six prestige. My request wasn't for the most power available short of Pun-Pun, or to heavily focus on one thing so as to be unbeatable in that area, nor was I just looking for the most multiclassed build possible. My request was more along the lines of "My werebear barbarian PC and his redeemed succubus wife have children, how can I assemble a character that demonstrates the capabilities of that mixed heritage, for when the kids grow up into playable characters?" After a lot of discussion a build was worked out: Bard 4/Barbarian 1/Spellsword 1/Dragonslayer 1/Rage Mage 2/Bear Warrior 1/Sublime Chord 1/Eldritch Knight 9. This grants BAB +17/+12/+7/+2, Charisma-based spontaneous casting of a small number of level 1-9 spells on the bard and sorcerer/wizard spell lists, a limited ability to ignore arcane spell failure, limited bardic knowlege, rage, the ability to cast spells while raging, and the ability to transform into a bear while raging, as well as some other minor abilities that aren't so important.
You might look at that class combination and cringe, thinking "What an overcomplicated, unfocused, dipped mess of a class collection." I look at it and think "This is Rachel Lovato, an energetic and outgoing young woman who's a capable warrior. She can draw on the bestial strength passed down from her father David, the compelling presence and magical talents of Seneca her mother, and the fiery temper she inherited from both. She prefers to get by with her cunning and charm, but she's a bit of a tomboy and likes a good brawl more than is proper for a lady. She hasn't seen as much of the multiverse as her parents, but she learned a little about everything from the stories they told her as a child, and it serves Rachel well in her own adventures." (I also think that from a raw power perspective, a single-classed Druid 20 would defeat Rachel easily.)[/sblock]
While I agree somewhat with 1 and 6, I am not sure if it should not be the case. Why should a cleric who takes lvs in fighter be better at casting spells or turning undead?