I put Thunderbird and Firebird on all of the lab PCs (2 WinXP and 1 Mandrake9), made them default apps, and hid IE/OE. These systems are mission-critical, but of course grad students use them to surf the web and check e-mail anyway. I took this step because I don't have the time or energy to constantly check the systems and keep them patched up and because other people use them all the time. You can cut your support hassles on Windows PCs down to the bare minimum by switching to Firebird/Thunderbird and then running an antivirus that autoupdates. I am sure Joe will argue about that statement, but he supports PCs for a living
I honestly dont see the point of Opera since Firebird is free, better supported, and has more features. I used to use Opera long long ago though when no other browsers had tabs.