Setting web based Gmail as the default mailto handler on Windows 7

You can, in fact set your default "mailto" tag handler to a webmail app, such as Gmail.

Run regedit and edit:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\mailto\shell\open\command\

To:
"C:\Program Files (x86)\Mozilla Firefox\firefox.exe" https://mail.google.com/mail?extsrc=mailto&url=%1

It works fine with Firefox or Chrome, haven't bothered to try IE, but I don't see why it would not work. There is probably some way to just set it to the "default browser" as well.