Regarding the actual playing of classes with alignment restrictions, I agree with Pentius and Tequila; I have never really played paladins until 4th, mostly because of alignments.
Not because I don't believe that they should have a code and stick to it, but because there was always too much DM control, and for years I gamed with a DM whose idea of such things was fundamentally different than mine, and I will add, often just flat out wrong.
The other part of my distaste for older paladins is that I honestly don't enjoy playing lawful good all that much. Under 3.x, I played a Paladin of Freedom (chaotic good) and really enjoyed that, and now under 4th edition, I have a Paladin of Kord who is fairly unaligned, but with what I would call a "good streak". Definitely not Lawful though.
Now this is almost entirely because of who I am in IRL. There are other classes with alignment restrictions that I've seldom, if ever, had alignment problems. Under previous editions, it wasn't hard for me to play a ranger. Or a bard. Or a rogue/thief. I can be good, I can be at least partly neutral, and I can be non-lawful. I still found them to be silly restrictions, but other than an incident with the aforementioned idiot DM and a ranger I played, I've never had trouble playing by the rules.
Paladins though - almost always a problem. I think some DMs see someone playing one as a challenge to *make* them fall from grace. Then again, maybe I just had bad luck with DMs during my D&D formative years.
Either way, the damage is done, and I am really take-it-or-leave-it on the whole issue of alignment.