The features are similar to what Google Video has and they will definitely increase the number of users because people like to read other opinions before trying something. Developers will be happy as well because they'll get much more feedback and they'll be able to improve the gadgets faster.
When you add a gadget created by a third-party, Google warns you about that. You have the option to disable the warning, although it's nice to know whether a gadget was created by Google and you can fully trust it or was created by independent developers and you should be more careful when you enter personal information.
You also have the opportunity to check the source of the gadget before adding it. This might be useful to see if the code contains anything dangerous (although it's complicated to decide that just by looking at the code) or to learn from it, in case you want to create your own gadgets.
After you add the gadget, you'll notice two new options in the menu: recommended gadgets and a link to the profile, where you can rate it and post a comment. If you like the gadget, there's an option to send it to your friends.
Update: Here's something I missed. If you add a new tab, Google gives you an option to populate it with gadgets based only on the name of the tab. This is a good way to build a homepage if you don't have time to try all the gadgets, as Google Blog says. Nathan Weinberg found out that "the system relies on many factors, primarily other people who have named their tabs the same way you've named yours, sees what gadgets are popular in that set, and gives you a page of them.". If you already have 6 tabs, here's a simple trick to create a new one (and a new one etc.): go to the personalized homepage and paste this in your address bar:
javascript:_renameTab(); _dlsetp('at=')
