It's really quite different from SoundCloud. Mixlr is about sharing live (streaming) music, while SoundCloud is about moving MP3 and WAV files about the internet. There is some crossover of course but a completely different focus.
I will be building a search/discovery mechanism when there is more music to search for and discover :-)
I think search/discovery is going to be what really makes this service special. I imagine one day being able to see all live music being streamed from venues in my area at the moment, maybe even a link to the venue, the band's homepage, similar acts, etc.
Right now you have a great tool that helps artists connect with their existing fan base in a way that removes previous technological barriers and streamlines the process, but what about new potential fans?
Secondly, I don't appear to be able to search for or find existing uploaded mixes, is this intentional or have I missed something?