Upgraded to Thunderbird 1.5. Nothing too wildly faboo in terms of feature improvements, but, then, a mailer is a mailer. It does spell checking, which is nice. My IMAP configuration still doesn’t work (which I think is a server-end problem), and Tagzilla doesn’t work under the latest release (an upgrade is promised soon, but that makes doing my WIST mailings more difficult), but overall, no significant problems so far.
UPDATE: IMAP problems are now solved — had to indicate it was an SSL connection, which used not to be true. Huzzah.