Lots of little gotchas if you don't at least do a fair amount of testing on Windows, since that's what most of your end users (usually) will be on. Things like

Lots of little gotchas if you don't at least do a fair amount of testing on Windows, since that's what most of your end users (usually) will be on. Things like "www-authenticate: Negotiate" in an SSO environment, people pasting rich text into web forms, handling environments with private certificate authorities, and so on.