The updated software is reportedly faster, simpler and less obtrusive for the user than previous versions. Specifically, Mozilla has ditched the “about:weave” config option from the tool, and has set an "interestingness" criteria that works like Firefox's Awesome Bar so that the most interesting of frequently accessed items are synchronized first. There's also a new incremental syncing mechanism that helps boost performance by breaking up data into "chunks" and synchronizing in the background.
The idea behind Weave is to allow a seamless jump from one device to another, so users can pick up their browsing experience, including open tabs and recently closed pages, from precisely where they left off. If you’re using Firefox 3.5 or greater on more than one computer, you might want to give it a try -- though you should keep in mind that Weave is still in beta and could conflict with certain add-ons.