I use them. But players can change when game progress without any problems. I kinda expect them to stick into it as part of their personality, that doesn't change unless there is reason. I usually ban paladins etc. anyhow. Mainly because one player in my group wants to play them as excuse being ass.
I use alignment based magic things, and detect-spells work etc.
Alignment makes it easier as Jon_Dahl stated before me to choose way to motive players to go for some adventure. I know if they want to play heroic fools or mercenery types or criminals or cultists etc. Alignment tells part of that, not everything, but if you put that and character class and chosen god (or not) into line, I usually get idea.
I don't ban evil or chaotic. I just want that players are mostly on same page. I could run pvp games but since that's not what they really want, I want to minimize their reasons to hate each others from bigger reasons like general world view/religion. That never ends well. Alignment is first clue to what is not going to work well as party. Same goes for "anti-classes" ake those opposing specific other classes (forsakers and the like).
Also if people write down CN I ask what are their defining personality qualities. I also tell them it's not same as insane, neither is neutral obsessed with balance. If they want those things they are part of those other personality qualities. I usually get things like out for myself, and my best pals at the moment, and greed, and in some cases some rebellion inticing idealogies. But that could be N or CG or NE or even CE. Alignment tells better how far character usually goes to get what he wants and how nasty it usually gets.
I always liked palladium alignment better. It actually gave some insight to that do/don't do this part. Not perfect but some much better defined than D&D ever. Too bad naming there was bit "unprincibled srubulous" .... or how was that spelt. That's reason to like D&D alignment better, unfortunaly.