If you haven't heard about SoundCloud, you will very soon. It has been described as the Flickr for professional musicians, or a Yousentit replacement, but actually it is much more than that. It is an easy way to digest and share new tracks with others, unlike how Splice has and is more focused on mashups of complete tracks. You could almost say that SoundCloud has analogies to Twitter, with the way the dropbox and your soundcloud inbox works.
Although, you could use it for partial tracks, as it provides you ways to privately share the original recordings. I do not see it provide the VST or ProTools/Logic settings to go with it. I find that to be the main issue with all these online collaborative services. I tend to do most of my work on my DAW and therefore making it hard to share with others unless hey have similar software that understands the configuration files. Otherwise we could spend hours tweaking configuration settings until everything is linked and buttoned up. Doing this without a settings template can be a real pain.
I find BoJam lacking in the same way. It is nice to have a way to see a video clip of the person I am jamming with, but how about exporting all his tweaks and adjustments in a format that I can easily integrate with modern DAWs. Most studios are not directly connected to the internet anyways, and I do not expect them to be. These computers are setup with a specific purpose in mind and have specific I/O points that are strictly monitored for security among other reasons.
I do find the SoundCloud interface pretty slick and I especially like the waveform with annotations. The first time I saw a waveform based audio player was with the launch of the bleep music store. It was an innovative concept then, and i still think it has a lot of merit today. More and more musicians are starting to get used to looking at their music in the digital domain as waveforms, FFTs, etc. It is a useful tool to be able to confirm what you thought your monitors were screaming about, by seeing a little blip show up on a frequency diagram.
Overall, I must say that SoundCloud is a welcome edition that is going to put pressure on others to improve the music creation and collaboration side of the business rather than the legally entangled delivery and licensing aspects.