I've always noticed that the tagging feature isnt really used by GS bloggers. most tags lead to gizzy. that being the case why not go for automated tagging, which is quite reasonable results-wise, and would give a nice way to link different blogs together.
one thing i feel that lacks GS blogs is a coherent narrative of the group... cross postings and so on.
there probably are solutions within vBulletin, but one pretty respectable organization that does provide free tagging for commercial use (for upto 30000 calls a day) is
here. I'm thinking of using my blog as a guinea pig at any rate.