London 2012:
OT: 19997
OT2: 20013
OT3: 13705 (at the time of writing)
Total: 53715 posts (thus far)
Beijing 2008:
OT: 17673
Athens 2004:
OT: 841
Can't find a thread for Sydney
(For the sake of completeness:
Vancouver 2010:
OT: 11192
Torino 2006:
OT: 495
Can't find a thread for 2002.
However, it's a bit unfair to compare winter olympics with summer ones)
Part of that's the fact that GAF's growing, but I think another part is the fact that this Olympics is in a reasonably convenient timezone for many and has an awful lot of interest for Brits who make up a reasonably large proportion of GAF's membership.
I would expect the next time the Olympics is in the US to beat that postcount. What I'm wondering is if Rio is 'near enough' to do so; it's a reasonable timezone for much of the US, but it's not actually within the US.
As an aside, it's amusing reading the scepticism in the closing pages of the Beijing thread:
In any case London could spend 10x less, like Greece did, and still have a great and artful ceremony, just like Greece did. However, what they had on show there at the closing, didn't seem promising. Looked more like an episode of "So you can dance", only with not as good dancing.