I'll start with the short version and give more info as this post progresses. Your time is almost up on this one, though. Go to Circuit City and look hard for this. They used to be all over the place but now there are probably only a handful on the clearance rack. They're marked at $39.99 but are actually less than $15. The hardware is junk: it works, but it's really basic. Maybe it'd make for a cheap alternative to an iPod Shuffle, but I've already got one of those. You can throw it away without qualm, although I suppose putting it in a Toys for Tots bin might not be the worst thing ever.
The prize is the card with the code for 180 downloads. Now, even when the package cost $40 this was pretty good, as buying the tracks individually would be $180 (the same as Napster and iTunes and essentially the same as Amazon's, Zune's, and Wal-Mart's stores). eMusic focuses on smaller labels, and in fact you probably won't find many, if any, Top 40 songs there. If you like alternative music you can find albums by bands such as Flogging Molly and MU330l, but their hidden talent lies in their Classical selection, which includes the Naxos label. Why is this such a good deal? Two main reasons exist. The first is that a lot of the albums are only five or ten tracks; you could download Shostakovich's 5th, 8th, and 11th symphonies by the London Symphony Orchestra under Rostropovich and it would only be 11 credits. Even at Napster/iTunes prices you're getting three (absolutely amazing) albums for the price of one. Now realize that you paid around about eight cents for each credit and your whole purchase just cost you less than a dollar (actually the same as a single Wal-Mart download). Secondly, even if you want something like J.S. Bach's Mass in B Minor which is 31 tracks. Instead of paying $31 through Napster or $13-20 in a store, you're paying about $2.50. The music is encoded in MP3 which means that it'll work on either your Windows Media Player devices or your iPod.
What are the downsides? Well, MP3s are twice as big as AAC or WMA files and so it could cause a budgeting problem on smaller players. However, you can convert the files without too much difficulty. You don't get the actual physical package, which would be nice to have. The lack of a booklet can be an important consideration, as the albums by Anonymous 4 include lyrics that you're probably not going to figure out unless you speak Medieval Latin. The sound quality is less than you'd get from an actual CD.
However, I tend to listen to music on my computer or in my car. The music is plenty rich as it is and I don't have the equipment to really gain more than a little bit more from a CD. The LSO Live and The Sixteen are two groups I've come to enjoy immensely, especially the aforementioned Shostakovich by LSO Live and the works of Allegri, Palestrina, and Victoria by The Sixteen. Really, check it out. I bought several and would give them as gifts if anyone I knew really liked Classical music and would download it.