Having promised it before, looks like Gmail has finally removed the annoying "on behalf of" message that sometimes appears when you consolidate multiple email accounts using Google.
The Official Gmail blog explains that you now have the option of sending mail via another SMTP server, which eliminates the "on behalf of" message. That might not always be viable, but if the address you're dealing with does allow it, it makes life much simpler and your messages less confusing. Hit the post for the full explanation. Thanks Danny M!
Send mail from another address without "on behalf of" [Official Gmail Blog]