This just happened over the weekend with my sisters '07 SES. Seems the cold weather made it worse (went from low 60's to high 20's) and caused the plastic to contract slightly. When driving it, I'd have to give it a pretty abrupt tap to get the pedal to move. It was fine as as long as you didnt completely let off the gas.
The throttle body/butterfly valve had so much crap deposited on them. I cleaned them on Saturday and she says her car is back to normal driving now.
I found whynotthinkwhynot's post
after a quick search