This sounds awesome. Detaching sets of bookmarks from a particular browser on a particular installation would be useful. Firefox sync works okay but it's still tied to just a particular Firefox account, doesn't enable keeping private life and work life separate yet still accessible.

If you're able to, please email me once the tagging is in place and I'll give it a spin! (contact info in profile, I'd be sad if I missed any of your follow-up submissions)

Also, please consider an annual pricing plan. Unfortunately, paying a monthly fee for bookmark management is going to be a tough sell (imho). I'd be willing to pay like $10-20/yr or so, depending on functionality and utility.