Just went skiing for the first time this year. Everything went fine for the drive there and the drive back. When I got back to Denver and stopped at the first light, instant stall. Next light, stall. Almost every stop from that point forward involved a sputter and stall. If there wasn't a stall, RPMs would drop slightly and the lights would flicker. Any ideas what I'm dealing with?

Here are the specifics:
2007 Impreza 2.5i
Manual Trans
21k miles
Had a half tank this morning and filled to full before I left.
Regular oil changes and maintenance.

I'm still fairly new to this car (2 yrs with just oil changes), and have been hesitant to do much myself due to the tight clearances in the engine bay. The majority of my car experience stems from a 1987 Volvo 240 that parks in front of the Subaru on most days. Any insight into general problems and troubleshooting that I should be aware of for this car would be appreciated.