So, far not many tips & tricks…
A nice fork of Sylpheed is Claws Mail which has more features.
I got some problems with an imap-courier server (on Debian woody and then sarge):
Sylpheed connects to the server, but I don't get my emails.
I first get the previous list in the INBOX, all other folders are empty and then I can't get anything anymore. It goes away like it comes…
When replying, if the quoted part is longer than 80 characters, it doesn't wrap the lines:
see http://sylpheeddoc.sourceforge.net/en/manual/manual-8.html (look for wrap)