I'm pretty average at FPS multiplayer, and pretty atrocious at RTS multiplayer.
I've logged over 400 hours into Team Fortress 2, and as it is the best I've ever done is ten kills and four assists. Most of the time I'm lucky to get two kills before being invariably backstabbed/headshot/blown into tiny pieces. I'm not terrible, but I rarely make it into the top quarter of the scoreboard.
Now, I can count on my fingers the number of wins I've had, combined, in every RTS game I've ever played. My strategies work brilliantly in skirmish against higher difficulty AI opponents, but in multiplayer, I've usually barely got my core buildings up before my opponent comes in with a massive horde of second-tier troops, razes my base to the ground and ruthlessly murders all my poor little worker units. It may be because a lot of RTS multiplayer boils down to who can set up their build queue the fastest, and I play RTS games to take a break from the frenetic twitchiness that is FPS multiplayer. As such, I get my ass handed to me. There was a time in the Starcraft II beta when I actually got a message that read "lolol ur micro sux noob".
Ah well, I like single player better anyhow.