StartCom is great, but 2 caveats: I found that StartCom's root authority is not recognized by some IE6 installs, and is still not recognized by Java (so applets, web start, java clients talking to your server may have problems ...).
The first time a user goes to StartCom on Windows XP on IE6, it will pop up with a "cert error". This is because the user hasn't recently updated their root certs through a super-optional Windows Update install. However, any subsequent loads will work as Windows will check and update their root certificates in the background.
