Hello there, first of all let me thank you for being part of our modest community...
Well although I've never used Google gadgets I did a little search and found out that these are chunks of code that one can put on their website to enhance the experience of its visitors... When added these chunks of code become different applications like calendars, games, picture galleries and stuff like that. Not sure but probably the type of code is mostly Javascript (client side scripting) which is ignored by typical web crawlers so it will probably not increase the site's rankings in terms of SEO. However if your visitors find these gadgets helpful and interesting that may result in an increase of the amount of visitors to your site. As far as I see there's a feature to create your own gadgets, (not very sure how that's done)... Hope the shared info is mostly correct and helpful to you... If something's incorrect please be welcome to post replies...
More info can be found at the Gadgets' page at:
http://www.google.com/webmasters/gadgets/