It has been 10 days now that I have been using Mail.app rather than Thunderbird and I am ready to uninstall Thunderbird entirely. While I am still waiting for GPGMail for 10.5 to advance beyond the beta stage I can use it as is. I didn’t really notice any difference in startup times between Mail.app and Thunderbird, but I did notice that it was faster at sorting incoming mail by rules and especially at putting the junk mail where it belongs. Thunderbird first loads all the incoming into the inbox and then sorts out junk mail and applies the other sorting rules. With Mail.app I don’t end up waiting for the rules to run before I can start weeding through my mail. I think the biggest thing, though, is that using Mail.app gets me into a position where I can more easily use other tools like the address book and it will, no doubt, facilitate syncing with the iPhone (if I ever get around to taking it out of the box and activating it – but that’s another story for another time.)