Single sign in

how about having a single sign in for different wp sites that use WordPress User Syncronization plugin. i am pretty sure that it could be very helpful. because of the different plugins that sometimes don't work well together, i (and i guess many others ) need to use 2 or more single WP sites to get one main site together. means all registered users have same information in all of the sites (using WordPress User Syncronization plugin) but then they have to login more then once as they are moving between the sub-sites.