To add to the other problems that people have mentioned, text selection is a little strange and putty doesn't pass along keys like "End" for some reason, which is useful in tools like less.

If you use git on Windows with PuTTY/plink it's also significantly slower than OpenSSH. I saw clones of a large repository go from 60 KB/s to 600 KB/s after switching from PuTTY to OpenSSH.