[pardon me if this come before, failed to find an appropriate topic]
in the light of Yahoo Pipes adding a Search Field on the Global Tags page seems to be would making it somewhat more useful than it is now.
basic search modifiers/operators like: 'quotes', ( parentheses ), + == AND, - == NOT are highly appreciated.
so that: tagA tagB - tagC
would return posts containing: tagA OR tagB AND NOT tagC
ex: wordpress.com wordpress - 'Britney’s Crotch', -- everything about wordpress.com OR wordpress except Britney’s Crotch
or: tagA + tagB - tagC
would return: tagA AND tagB AND NOT tagC
ex: wordpress + plugins - 'comment preview', -- search for all WP plugins except 'comment preview' one.
search results could be exported as RSS feed, while search conditions could be saved for a 'Tag Surfer' for people to watch for them (making the last much more useful too).
a bit of basic notion of English grammar would be desired of course too (single or plural, possesive forms etc, just look at this forum Tags page) but this one is rather difficult to implement I guess (may be there's an appropriate web-service?).