I have 46 bookmarks (and 74 tags) in Diigo and I’m finding it faster than Furl, less confusing that My Web 2.0 and more powerful than Del.icio.us. The network in Del.icio.us still makes it worth checking out but it isn’t my tool of choice for capturing research anymore.
Generally to be recommended.
Update: I now notice Techcrunch loves Diigo.
Double update: The scathing review I read was at Mashable.