Sad news today: Google has quietly advised that that they have ceased development of Google Browser sync and will faze out support.
Google Browser Sync, for the vast majority of people who have never heard of it nor used it, was/ is a Firefox plugin that synced browser information across machines, including bookmarks, cookies and passwords.
The folks over at LifeHacker are focusing on the bookmark features, but I've been a long user for the cookie and password sharing (I use Gmarks for bookmarks). To give an example when I was still using it (it has unfortunately never been available for FF3, but it does work in Flock and FF2) I could jump on my laptop and access a site I'd signed up to on my desktop immediately, without the need for new cookies and where applicable the password would be available on that machine. Notably as this was a Firefox plugin it was OS independent, and it made my switch from PC user to Mac user early last year that much more simpler as with Browser sync all of my passwords and cookies came across from PC to Mac. Another handy feature was the ability to continue sessions across machines, for example if I closed my browser now and switched to my laptop, on opening up Firefox Google Browser Sync would ask me if I wanted to open the same tabs I previously had open on the desktop.
Some have suggested that Google should open source the client, and it's a reasonable notion to point as I'm not sure I'd trust an open source platform to sync my passwords.Google Browser Sync is still available for Firefox 2 and if you are looking to swap machines, or if you buy a new machine and want an easy way of syncing your browser data, I'd recommend giving it a go while it's still available.