800 Giga Hash per second user just started mining at ...
There has been no official confirmation on who it is yet, but if you head over to BTCGuild and check on their Hall Of Fame page you will see a user, called 67117 that is mining at a ground breaking 800 to 900 GH/s (or 800,000,000,000 to 900,000,000,000 Hash's per second, or .8 to .9 TH/s if you prefer).