Lee Sedol isn't at the top of Go ratings. How would Ke Jie fare against AlphaGo? A match against the best human player would be a better test of AlphaGo capabilities.
Honestly that hundred point difference at the top of the Go ratings isn't really going to matter. At best, it probably means that the top player has a ten percent chance of winning a single game, instead of a two percent chance. I wouldn't be surprised at all to hear that AlphaGo is playing at a rating in excess of four thousand, and could be expected to beat the best human players 99% of the time. Frankly, my gut instinct watching the livestream is that AlphaGo is playing at such a high level that even the players at the top of the rankings are having ...
There have been a couple of brief discussions of this in the Open Thread, but it seems likely to generate more so here's a place for it.
The original paper in Nature about AlphaGo.
Google Asia Pacific blog, where results will be posted. DeepMind's YouTube channel, where the games are being live-streamed.
Discussion on Hacker News after AlphaGo's win of the first game.