After taking a lot of what different people have said about haste, considering different types of games, different types of casters, different situations, etc, and adding personal experience, I believe I have formulated my two cents on haste. Here goes:
For a wizard in most situations, haste fits into the grand scheme of things pretty well. It isn't too overpowered, but is still quite useful in some situations.
In the hands of a sorcerer, it is a little bit grayer. It isn't too difficult for a sorcerer to abuse haste if they aren't challenged in the correct way. But, in the hands of a fairly good DM, it is possible to overcome it (though doing so may involve tactics that annoy some PCs).
Items that have haste (wands, scrolls, boots, armor, etc) seem to be unbalancing. It's just too easy to use and abuse. Wands and scrolls allow it to be used too much and at any time needed (as well as by rogues). Clothing allows it to be used by any character at all whenever they want it. Combining these items with the previously mentioned abilities of spellcasters, it can become an easily abused spell by a party, leaving the DM no choice but to either a) live with it, and give the characters harder battles to even things out, or b) make all of their encounters have at least some aspect of them involve countering the spell (either with a counter spelling option, or by simply wearing the players down over the course of a long day with a ton of encounters).
So that's my take on haste, until someone can show me otherwise. My idea to stop haste from being a problem? No hasting items. An occasional scroll may be allowed, but definetally not a library of them. No wands, and definetally no boots or armor. As for weapons or items that store spells, I would probably have to test it out before I could make a good call, but I would lean against it.