Is still available or need to wait another batch?
They are under continuous production now. RS are manufacturing in China, Farnell/Element14 are manufacturing in the UK, the lead time is about 3 weeks at the moment. But some people on the Pi forums are claiming that they are only waiting a week!
The only unit currently in production is the 512Mb model B (revision 2, which has an improved board layout, including a power back feed via a powered USB hub!).
I'm currently using mine to learn OpenVG (like OpenGL but for 2D graphics).