Perhaps these are Londoners on holiday? - let me know if it's you!
Surprisingly, 24% of viewers use an Apple Mac (as I do) as Apple only have around 1.7% of the market share (2010 figures).
I'll take that to mean a greater percentage of viewers of this site have discriminating taste (you'd have to pay me to use Windows instead of Mac OSX)
The last 2 or 3 days (19th & 20th May) have seen most of the traffic