I love TwitterGadget as a fully functioning Twitter client within GMail. Back in the "good old" days of Twitter, we had IM integration so these sorts of tools weren't needed if GMail was a major part of your workflow. However, Twitter took that functionality (and Track) away from users in May '08, so we've been scrambling around to find the most efficient apps ever since.
While I think Seesmic Web has a great deal of potential, I'm still a fan of TwitterGadget plus TwitterSpy (which allows for semi-Track functionality based on the API… which is much slower than the original Track implementation). So, I've got a contstant flow of tracked items (my alma mater, favorite sports, business terms, ideas I'm interested in pursuing, my name, etc) on my GMail IM.
But why hasn't someone developed a GMail gadget for FriendFeed along the same lines as TwitterGadget??That would be killer and allow me to direct my Twitter, blogging (through Posterous), Facebook and FriendFeed accounts mostly through GMail.
Seriously, if you're a big GMail and Twitter user, give TwitterGadget (and TwitterSpy) a try. And if you're a developer, get on the ball and deliver my FriendFeedGadget for GMail. Thanks.