Re: Mmmmmmm, horse meat.
Yep, been using OpenJDK for a while on Linux without issues. It's nice to not have to manually go to Sun/Oracle's website to separately download it. (Gentoo's Portage system could install it, but it still required you to manually download it as Gentoo were not permitted to host mirrors of Java binaries.)
I do need it as I have 5 machines that use a JavaWebStart applet for the IPMI/KVM solution built into them. At work, there's some Dell machines with iDRAC that needs the same solution too. Both these work fine with OpenJDK.
I was curious though, what to the Apple and Microsoft users do? Turns out, there are some unofficial builds: http://stackoverflow.com/questions/5991508/openjdk-availability-for-windows-os
Use at your own risk of course, but sounds like it'll be less legal risk than JavaSE.