Usability 
SoundCloud is a Berlin based startup that lets musicians and bands collaborate and promote and distribute music. There are no upload file size limits and uploaded music can be shared anywhere including Twitter and other social media sites or embedded in any webpage using a widget. According to Wired, SoundCloud's freedom and flexibility have made it the preferred place for musicians to distribute sample tracks and interact with their fans, displacing MySpace.
SoundCloud also has apps for iOS and Android and desktop and mobile webapps that let anyone sample uploaded tracks for free and without the need to register.
The mobile webapp is new. SoundCloud created it after realizing that Twitter was driving a lot of mobile browser traffic to their Flash based desktop site. On the SoundCloud Blog, musician and SoundCloud product manager Matas Petrikas explains how the mobile site was built using backbone.js and node.js among other things.
Intended to be cross platform, SoundCloud worked flawlessly for me with the Android and Opera Mobile 11.5 for Symbian browsers. The site also rendered well with the WebOS and bada browsers but sound files didn't stream on either platform. WebOS reported an error streaming and bada downloaded the files without even trying to stream. Once downloaded the SoundCloud files played without problems in the bada and WebOS media players. The only browsers I tried where SoundCloud wasn't usable were Opera Mini and the Symbian Anna browser. Both were unable to load more than the top titlebar of the SoundCloud site.