I'm a baritone who currently studies voice at Amherst College in Massachusetts.
Amherst has a few choirs-
There's a Glee Club (all men) which generally sings old-time Amherst fight songs, etc, at college events. It's very informal.
There's a Women's Chorus- don't know much about it.
There's a Chamber Choir which has about 30-40 members. Generally does small-choir repertoire and goes on a major trip once every two years. I've only heard them a couple of times- although they're a little more serious than the Glee Club, I don't think it's that competitive to get into, as there are only so many singers at Amherst.
There's a Madrigal Choir, which sounds all right (I've heard better groups, I've heard worse)- I think they have 15-20 members, though I'm not sure.
In the spring each year all the Choirs get together and do a major choral work with the orchestra (Bernstein's Chichester Psalms last year, Beethoven's 9th the year before)
Also, there's a flourishing Jazz band program that is always looking for a few singers (I fronted a small jazz combo this year and it was amazing- I sang in about 5 concerts during the year and we recorded a CD- a lot of fun!). The fellow musicians in the combos are first-rate.
In terms of A Cappella groups, here they are:
Zumbyes (all-male)- by far the most popular- they have very impressive dance routines, generally solid singing, though a lot of people are put off by how popular they are- they've had their own catered parties and being in the group is a bit of a status symbol. Their shows are still worth going to. They're considered one of the top groups in the country (they've won several competitions and are generally considered in the same class as the Brown Derbies and the, in my opinion vastly overrated, Yale Whiffenpoofs).
DQ (co-ed)- Popular, generally solid singers, very funny skits, their repertoire is very eclectic (jazz standards, 70's rock, the hampster dance theme even). Some even think they're a bit better overall than the Zumbyes. I'd say they're pretty close, if not even.
Bluestockings (all-female)- pretty good, I've only heard them once. Auditions seem pretty competitive, but they're really not that popular.
Route 9 (all-male)- initially (even as late as the fall) they were pretty bad, but they've gotten a lot better. They do entertaining songs ("Cause I Got High", "No Diggity") and their shows are pretty entertaining.
Sabrinas (all-female)- don't mean to badmouth them, but they are not really very highly regarded. their last show was pretty good, but more for the skits than the singing.
What's the significance of this?
Basically, if you are looking for fun choirs that do something pretty serious once in a while, you can get into one of them pretty easily.
If you're looking for a good a cappella group, it's going to be pretty competitive. Zumbyes usually accepts about 15% of the people who audition, with the other groups ranging from a quarter to about a half. This comes from hearsay from people I know who've tried out.
If you're looking for a hyper-serious vocal education, you're going to have to be a bit more resourceful. There is little emphasis on technique in the choirs, and none really in the a cappella groups. This is a bit frustrating for someone (me) who is interested in a career in opera music, but there are a few options. I'm currently taking lessons with a freelance, semi-retired, voice teacher who's really amazing- I'd say he's just as good as my old teacher at Manhattan School of Music (who was also on faculty at Princeton). He also told me about a very small local opera company (the Valley Light Opera - www.vlo.org)- I auditioned for next season's production of "The Yeomen of the Guard" and managed to get a small speaking/solo singing role in it. Plus, there are group recitals once or twice each semester that singers can apply for (if they're taking lessons) and perform in.
Hopefully I can continually update this with more info about singing@Amherst- I'm only a sophomore at the moment.