My $.02 for what it's worth. I would definitely stop using IE--but agree with susato to keep it around for the odd site that needs it. (Thankfully, these are becoming few and far between.)
I found that Safari does not work as well on OS10.2 or 10.3 as I see it on 10.4. In my experience, after using Safari for awhile on the pre-10.4 systems, I began having problems with spinning wheels when I startup or shutdown. People have suggested various workarounds and fixes, but why bother when there are other browsers that work without having to do that??
For my eMac on 10.3.9, I'm very happy with Firefox--including the most recent update to Firefox 2.0. For my iMac (dv+; 450) which uses 10.2.8, I've found that Camino seems to work best--but I'm not sure (and am too lazy to run to the basement to check) which version of Camino I'm using on there.
But by all means, stop using IE! Even their own site (msn.com) will cause problems on a Mac!