Bookmark sync works just fine (i don't use the rest of the features) Rated 4 out of 5 stars
The only reason I installed this addon is that I have 100,000 bookmarks and was afraid to lose them, so I only use bookmark sync and that's it. I've had a few problems in the past and slightly more than usual recently, but nothing that wasn't quickly fixable by playing with the options in Xmarks options. So I still trusted the addon; but now I see all these negative reviews and am getting concerned at whether trusting this addon with all my bookmarks is really a good idea. I've just checked some folders at random and the store of them online at my.xmarks.com and everything appears to be fine. So I just wanted to say that I'm happy with the service still, and am just concerned by the number of negative reviews this addon has received recently. So negligible problems since upgrading to FireFox 4 (nothing a simple re-uploading to the server in the Xmarks options wouldn't fix) and I'm still using it happily, just with closer scrutiny.
So the core feature of Xmarks still seems to be operating as usual on my end.
And the web discovery features have transformed my web experiences in the past; for those I am eternally grateful.
I am concerned at whether anyone at Xmarks actually reads these reviews anymore, however, considering that no developer ever seems to reply any more. Perhaps it's too popular for one-on-one responses, but it remains a concern.