I get my Xbox back tomorrow and this will be the next game I pick up, the only thing I'm worried about is:
Do people camp with the grenades attached to walls and blow up others whenever they get near?

I do this on horde mode but I wouldnt worry about it in MP

Not too much. For the most part, most of the maps are pretty nonlinear, so people generally don't do that because they're not sure where the other squad will go. However, I can imagine a situation of 1v5 and attaching some grenades to nearby walls, and "holing" themselves in to create traps and lead the enemy to these traps.

It's nice the smoke grenades actually do something now. They don't kill, but they knock you down.

I whore this tactic out on Blood Drive, thers a crap ton of pillars and small corridors its easy for someone to get blown up by accident.

And even when all you have is smoke grenades its nice to have some sort of early warning system when your by yourself or sniping.