Just in case you are curious, I did your suggestion and did the math. It certainly appears that most fic posted to LJ is McKay/Sheppard. It wasn't nine hundred stories, but it's not bad for a prelim study.

I went through the sga_reader friendslist from July 28th to August 1st . I took note of the pairing of every fic listed and worked out the percentages. There were 141 fics examined. I know this isn't a huge sample size, so there may be further studies. I also might go and look through the sga_newsletter to see how close the percentages match. Any errors are totally my fault.

Highest:
Mckay/Sheppard: 43%
Gen: 18%
Sheppard/Weir: 9%

More here! (http://das-kabinett.livejournal.com/13768.html#cutid1)