Cache files
As fast as pages load nowadays, you don't lose much by flushing your cache files frequently. I hoard my history and cookie files, though.
I used to back up Netscape Mail by simply copying the mail folder to my backup. It worked.
It's not quite that easy with Outlook, but a utility called BackRex Expert Backup crunches a backup for both Outlook and all my IE settings in one step. Has worked pretty good so far.
