I feel like I'm constantly getting the stupidest goals scored against me that would be so easily preventable if I could press players without getting skinned every single time.
Try use only the good defending players (eg. Vidal, Chiellini, or Licht) for aggressive pressing.
When I'm defending in front of the player who's controlling the ball, one thing that I keep in mind is that you must always look to the ball. The second you lose track of it and wanders off, CPU will skin past you.
I'm no expert at FIFA 12 but this one little principle has helped me reduced countless of goals.
Look at what the new FIFA challenge is.
Edit: I'm actually enjoying the new defending system. Had great fun against someone playing as Barcelona online, constantly tackling all their players with Luiz Gustavo.

Once you get the hang of it, this year's FIFA is really enjoyable, absolutely harder, but I can say it's more enjoyable than last year.
Anyway, I know this has been said many times but Vidal really is a beast.