If you have a problem like I had "what was that site again, let's check the browser history..." and after wasting a couple of minutes realizing "it was not this computer, it is still open on my laptop", you really dont want to experience this again. Or you have a large bookmark collection what you dont want to keep mailing back and forth or or or ...
I was using XMarks for syncing my bookmarks only (I am a bit paranoid) on my own server. It was fine so far, occasionally it had some issues, but these were sorted - at least some of them quite quickly. Unfortunately using your own server did not let you sync open tabs, so you are stuffed again.
Then I tried Firefox Sync on Firefox 3.
I am using it now for a few months and it just rocks. I never had any issue. It will be integrated into Firefox 4 as described on here, but you can also get an Addon for Firefox 3 here. This support page describes how to set it up, it is very easy...
I started using it on my own server, as I am a bit paranoid. I changed now over to Mozilla's service and it works just great. You shouldnt obviously use it in conjunction with XMarks...
Some features to point out:
"Tabs From Other Computers": When you click at the single down arror on the right hand side in the tab area you will see this item.
Encryption is done by the client, so Mozilla cannot access and decrypt your bookmarks. Do I need to mention to keep your decryption key in a safe place?
Encrypted User Data The Firefox Sync Service encrypts User Data on your computer and uploads encrypted User Data over the network using SSL communication. We believe that user privacy is important, and we require that the User Data is encrypted to reside on Mozilla’s Firefox Sync Service servers. Those items you choose to synchronize across devices using Firefox Sync are examples of User Data that is designed to be encrypted before leaving your computer. These can include your browsing history, form history, bookmarks, saved passwords, preferences, and open tabs.