There are a fair number of browser based strategy games such as evony.com where latency is not really an issue. It's mostly a question of how to handle communication between back end servers and 'world' chat that's the real scaling issue.
It should be more than adequate for strategy or turn based games. Perhaps I should have been more clear that I was talking about latency sensitive MMOs, like shooters or anything where your position and movement in time are critical to the gameplay.
