There are quite a few forks out there already, mostly with slightly better user interfaces. None of them seem to have much traction though.

There are also some pretty good commercial alternatives although they get drowned out by all the free stuff on Google.

Already been done. Meet KiTTY:

http://www.9bis.net/kitty/?page=Welcome&zone=en

It's not nearly as stable as Putty though. It crashes for me a couple times a week (mainly when connecting to routers)