Sidebar gadget are often 'useless', as are many of the gadgets for other technologies (Mac, Google, Yahoo, et.al are included in this evaluation). I'm not saying there are not some useful once, but how many clocks, battery displays, and picture viewers do you need?
Anyway, I installed a very good one 
The "Calvin 'n' Hobbes" gadget, and I promised to myself I won't use it more than once a day ... otherwise I would spent all day just readin Calvin 'n' Hobbes comics. While on the topic: get the Complete Calvin and Hobbes Box Set, it looks great, very well done, and gets you all Calvin & Hobbes available. I got it as a gift from my wife and kids past Christmas - priceless!