Of all the hits my web log gets, a significant number comes from searches, and of all the searches, people land up here or here searching for alsa. Probably, the posts themselves are too outdated to be considered worthy of search; so here's a more recent opinion of alsa with Nvidia mcp51 rev a2 sound card:
As of 1.0.14, alsa works out of the box for this card. Even sound capture works! Although I must add that I haven't put it to a rigorous test. I tried making skype work with OSS emulation but failed miserably. (Anyone out there ? on AMD64 ?) So, if you are on a older version of alsa, simply upgrade to 1.0.14. Get the sources or just emerge it if you are on a Gentoo based distribution.