The upload process seems to be a tad slow, and the first time you use it it appears nothing is happening. Look to the bottom right, below your mix list, and you will see upload progress. They have an iOS application, which is a little flaky, and their website works similarly on iOS. Both are just for playing. There does not appear to be a BlackBerry application. Unsure about Android.
I have done three mixes so far. Nothing great, but mixtapes were not quite my specialty. These have some decent songs, and tend to stick to a theme nicely. The "Strange Love" mix is my favorite. NSFW, by the way. Find my profile here.