I use Gmail as my primary email, but I also have a Google apps account that is forwarded to my Gmail. On the computer, I have it set so that I can compose a new message and change the from field to be either from my Gmail account or my Google apps account. This way I keep everything in my Gmail account (so I can search for both sent and received messages later) but make use of both email addresses.
On my Droid X, I set up both accounts in the Gmail app. Now, from within my Gmail account, I can compose a new message from either my Gmail or Google Apps account. That part is good, but the same functionality does not carry over to replying to messages. If someone sends a message to my Google Apps account, I receive it in Gmail but when I hit the "reply" button I can only send from my Gmail address. Is there a way to reply, from within Gmail on my Droid, from the Google Apps account?