mate of mine has one and he hosts some mixes on there, its a bit limited though and you have maybe 3 hours worth of music before you have to pay. I find sites like Reverbnation a much better choice, its all free and has no restrictions
they have an iPhone app as well, which is very good. Best thing I like is the ability to comment on various time stamps. Also a lot of forums has tag enabled for sound cloud so taht it can display the controls and waveform.