I have it running (sort of) on 7-STABLE; the network does work for me with the default settings. My issue is that although the kernel module loads when the program is compiled, subsequent kldloading locks the system solid. The tools also give an error.
I use Vbox on CURRENT and have no issues with connecting to the network via NAT. I had to recompile my kernel to remove INVARIANTS and WITNESS to avoid crashes. Overall I'm very impressed with the speed and responsiveness of the network provided in Vbox.. I too await bridge functionality.