When I play online either I get absolutely owned or do reasonably well, but nothing spectacular. I haven't played online in a while so probably it would be a little more unbalanced nowadays though.
When I play against my friends or my housemates I dominate them from start to finish. We play Halo and I set myself ridiculous challenges like three on one, and I'm only allowing myself to use the pistol, and I get through the whole round without dying. We play CoD or Modern Warfare and I only use the sniper rifle, free for all, and I rack up more kills than the three of them combined.
I think I'm a pretty good gamer, but I don't challenge myself often, so when I come up against gamers who do I often get my ass handed to me, but when I play against my housemates or friends who are all 'W007 PWNING NOOBS RS TEH AW3SOM' and only play multiplayer CoD I basically wipe the floor with them. Too much practice.