I'd like to keep my bookmarks synced between different browsers, computers, and operating systems. What's the best browser plugin or other solution to keep my bookmarks synced between all of these?
I use delicious http://www.delicious.com/
and whatever browser plug-in I need to access easily.
I personally prefer to use Google Chrome, which supports this natively. As a bonus, your bookmarks are also available within a special folder in Google Docs.
Options -> Personal Stuff -> Sync:
This does not synchronize your history or saved passwords.
Since Firefox is still the default browser in Ubuntu, I think it's worth mentioning that Mozilla also developed a syncing add-on called Sync. Firefox 4 will have Sync built-in.
Ubuntu One can also sync Firefox bookmarks, but you have to install an add-on called Bindwood first (there's an "Install" button in the Ubuntu One client for that). Unfortunately, service uptime is not so good at the moment.
Xmarks isn't closing down. Check this blog post - http://blog.xmarks.com/?p=1988. So, do you really need any alternative? =)