Hi
All I can say about cross-compiling is that I tried to compile sparc64-binaries on a amd64-PC and that resulted in a huge mess. I think I will give it a shot again sometimes in the future but for the time being I don't feel like telling other people to do the same.
I installed Gentoo a few weeks back on a netbook having an Atom 270 and it worked fine - it just lasted 4 times longer than usual, but it was still acceptable.
What you could do instead of cross-compiling is to use "distcc" when you emerge something. "distcc" is fully transparent to "emerge" and it spreads out the compilation as well to other PCs connected to your network.
http://www.gentoo.org/doc/en/distcc.xml
I used it on some PCs and it worked fine and it is for sure easier to use than cross-compiling, especially once you have a working environment.
The guide for distcc for cross-compiling:
http://www.gentoo.org/doc/en/cross-compiling-distcc.xml
Hope it helps!
