Google mail is now even cooler!
I just discovered that if you go Settings->Accounts, you can choose to add other "From" addresses to send mail from!
This is fantastic - if you have another address that forwards to your gmail, you can now respond from that address - completely transparently! No advertising, no google branding *anywhere*.
Even if you don't - you can set gmail to pull your mail from elsewhere, then respond to it from that address - great for a temporary solution while you're on the road...
I'm in love.