Yesterday, I got a Foursquare friend request in the notifications panel.
The only running services at that time were, I believe, the same that are running now. Definitely there was no Foursquare service running. I hadn't used Foursquare in weeks. From Settings:
Google Services (GoogleLocationService)
Google Services (Cloud to Device Messa…, Google Messaging Ser…)
I was logged into Google Latitude.
By what mechanism did the friend request reach the notifications panel?