[iNik]

Here's a plug-in to handle that using Google Notifier. Pretty bare bones, right now. Just looks for messages prepended with "--" and goes from there. I'll probably put a little more work into it so that it works similarly to the Mail rule's script and checks for valid senders, etc.

(* Plug-in for Google Notifier to search for OF task messages and process them *)

on NewMessagesReceived(messages, fullCount)
  repeat with msg in messages
    if title of msg begins with "--" then
      tell application "OmniFocus" to tell default document
        parse tasks with transport text title of msg
        
        -- Since Google Notifier doesn't pass the whole email, we only parse the subject and then append the rest as a note
        set newTask to item 1 of result
        set note of newTask to summary of msg & (return) & link of msg -- Links are wrong for hosted accounts
      end tell
    end if
  end repeat
end NewMessagesReceived

You can also use Gmail's RSS feed to do the same thing using a utility like Proxi. This has the advantage of not re-processing already read emails, as Notifier will. (It runs all its rules on all incoming messages each time it starts up -- a giant PITA)