Just to get opinions on the way, you are free to take a look at the devel site for 5.1. This won't always be open, sometimes there will be an htaccess on it under certain condtions, but most of the time anyone interested can wander over and take a look.
I'd appreciate it if you didn't ask questions on the devel site, keep them on this forum. But you are free to comment, critique, question, etc anything you see over there. To keep everything centrally located, you can just reply to this thread for anything concerning 5.1.
Remember not all functions will work during development so if you get an error at any point, I probably know it's broken[]/w3timages/icons/wink.gif[/].
Keep your eye on the CHANGES file so you can see what is actually being done, so you'll know what to look for. CHANGES can be found at
http://www.wwwthreads.com/changes.html. The devel forum can be found at
http://www.wwwthreads.com/cgi-bin/devel/wwwthreads.pl.