I usually get caught when fast forwarding when they show previews of other shows and they have that TV 14 or whatever in the top left during the preview. That's usually what you see when you come back from a commercial.
they do make it easy to know when the commercials are coming. I get ready when the bug in the corner goes away and look for the rating taking up 1/3 of the screen when they come back....now if we could only automate the fast forward to jump over the whole break.