Typically, portable applications go hand in hand with flash/thumb/pen/USB drives, but this is not a requirement.
The flip side, uninstalling, is another advantage of portable applications. In contrast, it can be next to impossible to erase all traces of a normally installed Windows application.
Thunderbird is the best e-mail program for Windows users, and the portable version is the best version of Thunderbird.
On August 31st I explained why I think Thunderbird is the best client-side e-mail program for defensively thinking Windows users (see ).
On looking at the mail storage links I noticed that Ubuntu made a huge change that broke all my folder allocations.
I use Ubuntu at home and Portable Thunderbird at work where I use a Windows box.
There doesn't seem to be any portable TB 1.5 release available yet, except RC1. T-Bird NNTP reader doesn't really update Maybe it's me. I have Thunderbird set to check GRC new group every 5 minutes. I sit here looking at and responding to email in various "Lists" located physically above the GRC newsgroup.