For now a tag submission page is available at http://blockchain.info/tags. Also for a bit of geeky fun I indexed the addresses contained in signatures from bitcointalk.org example: http://blockchain.info/address/1H4sGgNSRvRuiUsbucsQBNFWhZcLnL2KW1

It doesn't include up or down voting as the tags in this context probably serve a slightly different purpose than your original idea giszmo. Which was to allow people to tag addresses as belonging to scammers, add comments etc? While I could see this being useful in some situations it has the danger of morphing into a blacklist which in my opinion is a bad idea all round.