- Thunderbird: C:\Documents and Settings\user\Application Data\Thunderbird\ and change the Path location in profile.ini, and every path contained in prefs.js (or user.js?) in your profile directory to match
- Palm Desktop: //HKEY_CURRENT_USER/Software/U.S. Robotics/Pilot Desktop/Core
- Trillian: Preferences->Activity History->Save History to...
- Firefox: Stored in C:\Documents and Settings\user\Application Data\Mozilla\Firefox\, but practically the only thing worth moving is your bookmarks. You can specify the location of your bookmarks by setting 'browser.bookmarks.file' to the location of your bookmarks file in about:config (update: tried this and it didn't work. I may just wind up making Linux use a symbolic link to the bookmarks file). I tried moving the whole folder, but there are so many places you have to change the paths to extensions that I didn't get them all and the browser would freeze on startup. It would be nice to be able to share cache, cookies, and saved passwords between Linux and Windows, but it seems that's more trouble than it's worth. Firefox doesn't use relative paths in enough places (with extensions in particular). Though, extensions are often platform-specific, so it's not possible to share those anyway. Also see http://kb.mozillazine.org/Roaming_profile.
- K9: Go to the statistics tab and click "Change data storage location".
The goal of all this is to have as much as possible shared between my Linux install and my Windows install. Unfortunately, since I use K9 on Windows, I connect to my mail servers through localhost, but on Linux I obviously don't have it set up that way, and included in the profile I'm sharing is the connection info. So if I change it to match my Linux install it won't work on Windows, and vice versa. Argh. But since TextDrive is about to role out service-wide server-size Bayesian spam filtering with DSPAM, I won't need my local K9 anymore, so I'll switch things to use my POP server directly.
You can also just use Portable Firefox or Portable Thunberbird