When you're at the club and the chairs and tables are all too close together, and you see yourself (or your sim) having a route-fail tantrum about it.
When you can't go anywhere or see anything on tv without assessing the architechture! (Incidentally the new decor in House the other night that he kept commenting on was very nice). I never used to notice things like that so much. Sure I'd see a nice house that I wanted to build, but now, it's like the architechtural features are the focus of any camera angle, rather than the actors in the middle of the screen!