Firefox 2 Beta 1
Transferred from Netscape 7 to Firefox when it was still at the Phoenix Beta. Liked it immediately, faster, less bloat and way more secure than IE. I just progressed with it - I do have Firefox 22.214.171.124 loaded, just in case I run into a problem with the beta but so far, with both Bon Echo alpha and FF 2 Beta 1, I haven't had to.
I still use IE to check Windows Update but nothing else. (yes, I know there is a Firefox extension!).
And I have used Konqueror on SuSE Linux. I like the integration (equivalent to Windows Explorer and Internet Explorer) but overall, I prefer Firefox, teamed with Thunderbird and Sunbird, of course.
I can also recommend Firefox Portable and Thunderbird Portable - a USB memory key is a lot easier to carry than a laptop!