eMusic is a music subscription service with a business model fundamentally different from Rhapsody, Zune Pass, or the now-defunct Yahoo! Music Unlimited. While the latter subscriptions allow unlimited access to a DRM-laden library of major label songs, eMusic offers a restricted number of downloads per month, which are in plain MP3 format and can be kept even after the expiration or termination of the subscription. eMusic deals exclusively with labels for independent artists, partially as a matter of brand identity, and partially as the group willing to accept eMusic's relatively low prices.
While eMusic's former business model offered subscribers unlimited downloads, this caused a great deal of trouble in practice. People would subscribe, download everything they possibly could (sometimes with the help of automated tools), then cancel the subscription, re-subscribing to download all the new music on the site once every few months. The result was eMusic's royalty payments being dramatically lower than expected, very little profit for eMusic, and a great deal of animosity by "honest users" who maintained their subscriptions as long as they were interested in the service at these "hit-and-run subscribers". Even these faithful users tended to download somewhat more than eMusic was planning on, but raising the subscription price above $15/mo would drive users away faster than revenue would increase.
eMusic therefore had to shut down for a time to introduce a subscription scheme similar to their current offering, although prices and quotas have been tweaked repeatedly throughout the site's history. They offer a limited number of downloads per month with no rollover; the download counter resets every 30 days, causing the reset date to change every month or two. eMusic is very open about their reliance on the resulting breakage to fund their business model; artist royalties on a download frequently exceed the average value of an eMusic download credit because they are divided on the basis of a percentage of eMusic's profits, divided evenly per download.
People who already have eMusic subscriptions can buy booster packs, virtual packages of extra downloads with a longer expiration date than the montly quota. These are generally used to round out the last few tracks of an album one doesn't have quite enough credits to download all of, although they can also cover for that "gotta have it now" feeling when something desired comes out and it's too long to wait for the next refresh. These booster packs cost two to three times as much per download as eMusic's subscription plans, as users who use booster packs do not generally produce breakage. Booster packs originally had no expiration date; this was changed to a one-year expiration date, and most recently a three-month expiration. eMusic relies on breakage, but does not cheat to attain it; downloads are always used in the order they will expire, so a user with a montly subscription and a handful of downloads left over from when booster packs never expired will not use those booster downloads until the subscription downloads are depleted.
eMusic's plans vary. New users can select from three monthly plans, which offer 30, 45, or 75 credits per month. From there, however, users who have been on the site for an undisclosed amount of time can switch to a "Base" subscription that offers a mere 10 downloads (as a way to keep users who are starting to experience burnout). Users can also sign up for annual plans, which are offered at a 20% discount in return for being locked in for a year. Users of the largest plans are invited to switch to the eMusic Conniseur plans, which offer 100, 200, or 300 downloads a month. These plans cost more per credit than do the annual plans, and they cannot be made to go annually; again, eMusic does not anticipate breakage here. They are intended for eMusic's true addicts, and they find some customers.
eMusic is highly recommended for people interested in finding new music and willing to accept the lack of major labels in return for wide variety and low prices. Their willingness to change their business model and subscription offerings speaks well of their stability in a changing market, although it also runs the risk that a subscription could be pulled out from under you. If that happens, though, you still always have what you already downloaded, and the lack of DRM guarantees that will never be revoked.