In Mail OS X 10.6 one of the changes is how an email address is copied to the clip board. By default in 10.6 when you copy and paste an e-mail address you get the output in "Name " . Before the release of 10.6 you could just copy an email address in Mail and when you pasted it you would just get "firstname.lastname@example.org."
If use use Mail.app like I do and use the copy feature to move e-mail addresses around, and are frustrated by this new format then I have a fix for you.
The developers of 10.6 build in a terminal fix to get the paste back to the way it was before. The fix is a real simple one.