Workaround for flagging messages?

I'd like to be able to flag messages on my iPhone so I can follow-up later on another computer. Unfortunately, the iPhone doesn't support flagging.

I've tried moving them to the Apple Mail To Do mailbox, but I can't figure out how to get that mailbox to show up on my desktop.

Does anyone know how to make that work, or have some other workaround for flagging messages?

(I use an IMAP mail server. I also use MobileMe for syncing, although not for email.)