if you are not a developer yourself i would suggest
http://www.pligg.com/
not only is the base script really good but they have a built in framework for plug ins
and have focused on developing a plug in marketplace
so you could buy the plugins to get the functionality cheap
they have a new jobs forum so you could get someone to custom code it
the mod to the current my diggs functionality could be modified to become my bookmarks
you would have to make the url database field indexable, and write a search for the submission (to find previous submitted bookmarks) and then trigger the voting/rank up functionality that exist
but that not really that hard
for sync i would suggest looking at the new ie 8 weblettes (sp) they look like they can provide the functionality you would be looking for.