Maybe it's a little unfair, but I had the same problem with For Your Consideration that Theo Panayides did: "none of the film clips feel like they belong to a film one might see today" - the film-within-a-film looks completely bogus. Not surprisingly, this was also my problem with Christopher Guest's The Big Picture. Anyway, I was reminded of this while watching The Sopranos from a few weeks back: the scenes from Cleaver - Christopher's "Saw meets The Godfather" exploitation flick - did manage to approximate the look and feel of a cheapie horror movie.
So, here's the topic for discussion: what are the best and worst films-within-films? Or (more appropriately for this blog) the ones you like the most and the ones you like the least?
Off the top of my head, my favorite might be Habeus Corpus from The Player, because I think it's a pitch perfect parody of the glossy, Presumed Innocent-style message thriller. It isn't realistic - that is, it's a little too knowing - but the exaggeration fits right into the overall mood of the movie.