Oh man. I just got Xbox live a few days ago, and started playing SC:PT online. It's so awesome. Anyway, i gotta stay of it for a few days. Here's why.
Basically, you play Spy's or Mercs.
The Mercs have two new vision modes, ElectroMagnetic Tracking mode, and Motion Tracking.
The only realy way to spot a spy is with the motion tracking, because they are pretty much invisible. So i played like this pretty much straight for a few days, with this red fuzzy motion tracking crap all over my screen. Now my eye is all bloodshot and one side of my head is in major pain. So i shouldn't really be typing here. but hey.
check out what i mean
http://www.splintercell.com/us/fullflas ... art=online
then click vision modes, then motion tracking on the right.