They're not technically crooks because they operate through a loophole in Russian copyright law...while it's illegal to sell an unlicensed copy of a CD, the selling of the data on the CD is not properly covered by any current legislation. As a result, allofmp3.com has the same type of license that a radio station in Russia might have.
The service they provide is exactly what online vendors of music should be doing: a comprehensive selection of music available in a wide range of un-DRM'd formats and bitrates charged at a very reasonable rate per MB downloaded. I'd be happier about using allofmp3.com if I knew for a fact that they do provide proper compensation to the artists and songwriters/producers who actually made the music though. It's not clear if the license they have provides for proper royalty payments and while they maintain that they voluntarily send payments to artists, the veracity of this claim is unsubstantiated.
Edit: Just went back to the allofmp3 site for the first time in over a year or so and discovered that it is apparently no longer possible to use the service unless you have a Diners card. Guess PayPal, Visa/Mastercard, and AmEx decided that they didn't want to do business with them anymore which certainly makes the site look much shadier than it used to.