When I found out and posted about the Sandbox CSS competition, I feared that it would increase my curiosity about the Sandbox theme sufficiently that I’d create a new WordPress blog to play around. My fears proved to be accurate; I just created Just a Sandbox.
It’s hosted at JustFree.com, which is currently free of cost and of ads. On the basis of a little Googling and clicking around, I’d say that the best account of what JustFree does and doesn’t do for you is Robert French’s post (and the subsequent comments, especially #2).