20090915 Tuesday update: I upgraded to 10.6.1 a day or so ago. Now this feature is working right again.
I upgraded to Snow Leopard this past Sunday. Yesterday, I ran into a totally new problem all day with Mail.app: It ignores the following preference:
Preferences | Composing | Send new messages from: <Account of selected mailbox>
If I set this to a given mailbox, that works, but choosing “<Account of selected mailbox> does not work. Instead, new messages go to the first account in the list on that same option button, which happens to be my personal mail account.
As a result of this, I sent tons of work email from my personal account yesterday. I noticed it on a couple of messages and fixed them as I was writing them. I chalked it up to user error at the time.
So far, I’m not happy I upgraded. That is, the upgrade hasn’t touched me in a way that outweighs this problem and the lack of support for Sharpshooter 0.5, necessitating a Sharpshooter upgrade.