I love that Gmail is adding a massive amount of functionality to its service via its Labs area (which allows you to test new features). In the past several weeks, we’ve gained the ability to send SMS chat messages from Gmail, to send video messages and to create to-do lists. I can also access Google Calendar and Google Docs data from small widgets in my Gmail sidebar. And today, a widget has appeared that may let me to close yet another tab in my browser window: TwitterGadget.

While TwitterGadget isn’t made by Google (or Twitter for that matter), its creators are taking advantage of Gmail’s ability to add third-party widgets (similar to what Remember the Milk has done). What you get is a small widget sitting on the left-hand side of Gmail that allows you to not only send tweets (Twitter messages), but look at all of yours. Yes, this gadget includes your friends’ streams, a replies tab, a direct message tab, a favorites tab and an “all” tab.

You can also easily add select symbols to your tweets from a drop-down menu in TwitterGadget. Maybe you’ve seen these before on Twitter but didn’t know how to make them — a heart, a star, a moon, scissors, etc — with TwitterGadget they’re just a click away. Another nice feature is that you can set the rate at which it refreshes your tweet stream.

The user interface of TwitterGadget could use a little work — okay, it’s ugly — but it’s very functional, and it’s also very responsive. I’ll take that over beauty any day (well almost any day).

Now I just need a way to combine Google Reader with Gmail to make it the ultimate time-suck web site.