Good things about eMusic:
1. They've got back-catalogue from pretty much every major indie label. Drag City and Sub Pop are notable exceptions. You want all those Portastatic or Xiu Xiu records that all sound exactly the same as one another, but don't want to pay full price for 'em? You can get it at eMusic.
2. You get 50 free downloads before your membership kicks in. With that fifty I grabbed a ton of live Hawkwind stuff and some great records by Jack Rose, the Diplomats, and Makoto Kawabata and Richard Youngs.
3. 90 downloads a month costs only $20. Or seventy bucks less than iTunes.
4. They've got the Chrome Box. Early Chrome records are impossibly hard to come by now. Go look on eBay; I'm sure you'll find a copy of Blood on the Moon going for some ridiculous amount. You can buy a cd with great early album 3rd From the Sun and some later inessential shit for only $199 through Amazon. I got both those records plus like four more through eMusic, and still had enough downloads left over for five more albums.
Bad Things about eMusic:
1. No major label participation whatsoever. TVT and Koch are as big as it gets. This of course leads directly to...
2. A horrible selection of rap/hip-hop. Other than Lil Jon, the Ying Yang Twins, the Diplomats, and the last two Goodie Mob records, pretty much all rap you can get on eMusic comes from unknowns. If you want to download those two good Dem Franchize Boyz songs, you'll have to look elsewhere.
3. Although there are dozens of records I am interested in hearing, there are very few that I'm actually excited to download. They do have some excellent stuff - the new Excepter ep, the entire catalogues of Robert Wyatt and the Minutemen, etc. - but I had a hard time finding stuff I'd be willing to pay full-price for in stores. eMusic's useful for sampling stuff, but you're not very likely to find that one specific album you most want to own at the moment.
4. They didn't credit me for my 50 free songs when my wife signed up. I sent my wife an invitation, she joined, and I still haven't received the 50 free downloads they promised. Assholes.