The current Samsung WebCL prototype works only on Mac OS X and Safari, but there is also a Windows (32-bit) version for Firefox 4 from Nokia. It is far from being mainstream, and there is a good chance that you can't try WebCL because of the limitations of the feature at this time. However, if it works, you can use it for Bitcoin harvesting - as suggested by Nokia - and generate about $10 per day. Samsung has posted two demo videos that showcase the opportunity, which is impressive.
There is no information when WebCL could be generally available, but we know that it took WebGL about two years from the first meeting to the finalization of the standard. We are just in the beginning stages and there is no reason to believe that we will see WebCL apps anytime soon. The outlook, however, is fascinating.