I've been using Xmarks now for ages (previously foxmarks) and I find its provides the perfect, bookmarks solution I was forever longing for!
Now, no matter what computer I use in our house, I open firefox and my very latest bookmarks are there exactly as the last machine. I find it very useful if I'm hunting for stuff too, as I can use a computer, and then switch to a laptop and get comfy on the sofa and read information I've bookmarked.
It works outstandingly. I seriously, seriously recommend xmarks. It also works with googles browser, safari (win/OSX), and firefox (linux, unix, OSX, windows), and I think it also works with IE too.
Currently I use Safari on my Imac, and firefox on windows and linux laptops and computers, all without problems. I even have xmarks running on safari and firefox on my Imac without an issue. I also use it on firefox installations I have running virtually using Sun Virtualbox.
Its absolute genius and I really don't know how I managed before I stumbled on it ages ago.