Polymorph - It occurs to me more often than you can imagine how truly blessed I am not to have players that are truly munchkin, rules lawyering, powergamers. I don't have a problem with it simply because this is a spell nobody bothers to use anymore. It now occurs to me that perhaps my players are too old, staid, and (dare I say it) unimaginative to really get creative with possibilities anymore.
I can see the problems inherent in the spell, however. Heck, I saw the problems with it even back in 1E days when people would pore over monsters looking for something INSANELY powered that wasn't more intelligent than their character.
There was mention of not being able to polymorph into anything you haven't actually seen. What's wrong with not being able to polymorph into a form that you haven't actually RESEARCHED instead? You know... just tell the DM what forms you want to have available for your PC, let the DM review all that that form is capable of as well as its limitations, and then the PC adds it to their list. If the form is for some reason too unbalancing then the DM simply disallows it until the PC is higher level, limits the duration of the change, EXTENDS the duration perhaps. It seems to me that CR should already be a good rough guideline for limiting what a PC can polymorph into - a creature of CR = LVL? CR x and no higher? Etc.
Antimagic Field - Another non-starter for me - it simply never comes up so I never have to even think about it. But again I can easily see how it's problematic and wonder why, oh why wasn't it just FIXED? If not in 3.0 then in 3.5? I've said for YEARS now (not terribly vocally or often, but well before 3E) that the spell levels and descriptions are the part of the game in need of the greatest overhaul. In point of fact I recall clearly being disappointed that the 2E revision failed to do anything in that regard and saying as much until 3E at last made some efforts there. I would very much be interested in seeing Chris Perkins 20-level revision. I've begun work along those lines on more than one occasion but abandoned the project as just a bit too much work. (I stopped wanting to rewrite the entire PH a long time ago. Call me lazy if you like.)
Floaty Shields - First I've ever heard this particular exploit. I'm fairly sure I'd just house-rule it to have them function much as a Dancing weapon including both the need to have it in hand at the start of the fight and its cost (as +4 bonus, not +2).
Raise Dead penalty - It sounds interesting but I have long advocated handling dealing with PC death issues from a much more role-playing standpoint, not by throwing rules at it because it addresses the symptom, not the cause of the disease.
20 level spell system - I would VERY much like to see it and hear some testimony on its strengths and weaknesses in actual play.
Ban stat-boosting items - Again, no problems here so no adjustments necessary.
"Smoothed" hp - I LIKE a decent range of hit points in PC's and DISLIKE the more "epic" leanings of the system already (I refuse to even TOUCH epic rules for my games).
Action dice - I prefer to think that there are better means of bettering the game than adopting a more game-ist approach to play. In any case it's a solution that's in search of a real problem - IME anyway.