It's something that I use everyday but hardly ever actually see:
It lets you sync bookmarks and favorites of all your PCs or laptops once setup it just sits there doing it's business, you can create sync profiles like Work/Home and select folders and individual bookmarks that are only synced to that profile (so that P0rn folder doesn't end up on your work PC, not that I have one of those, really!).
It used to only work for FireFox (hence the name) but they now also have an IE version (and there's also a Safari version, all these can work concurently with eachother), the news was in their blog .
And even if you're on a PC without such a browser or cannot install the add-on or software then you can still go to the FoxMarks site and access your bookmarks from that site (it's what I do on my mobile phone or on a public computer)