If you play on FICS any, ficsgames.com is a handy site for finding old games and spying on potential opponents.
For example, you’re probably sitting there saying to yourself “Hey, I hate that Liquid Egg Product doesn’t put chess on his blog anymore. To get revenge, I’ll challenge him to a game on FICS and beat his army up and down the board.”
What you can do is visit ficsgames.com, and check out liquideggproduct’s statistics (or whoever your hated enemy is) like below:
Clicking on the standard Charts link (as shown in the second diagram) will show you graphs of your target’s rating, favored openings with each color, and other stuff, like the one below:
And then when you looked at my openings, you’d say “LOL, he plays the Pirc/Modern; I’ll just establish a huge pawn center and use my space advantage to squeeze him to death.”