I've been noticing that a lot of the authors I work with, and a lot of the self-published books I read, like to sneak this line in. Something weird is happening, or somebody shows up at a suspiciously convenient time, and all of a sudden the deus ex machina kneejerk-reaction sets in, and a character says "It feels like we're in an old B-movie! But we aren't! This is real life!"
I'm not going to say that this is always bad, or that it can never be used effectively. Because I don't say things like that.
There are a couple reasons, though, why I think that this technique is usually a bad bet.
1. It's overused. So overused, in fact, that even if you've used it well, the reader is going to wince and hate it and not appreciate that you are the one person in the last dozen books they've read who actually really got some technique and nuance going with it.
2. It's cheap. It says "ignore the fact that what I just wrote is highly unlikely." It's not a terribly persuasive argument, but it does glue a patch over the rough bit by saying that the author (via the character) recognizes the logical or scientific leap that has just been taken and assures you that it's okay.
3. It betrays the author's discomfort with what he's written. If you've written the situation, the setup, and the book well enough, the reader is going to go along with you because you have carefully suspended his disbelief in the pertinant areas. If you haven't, like if you're 200 pages into what appears to be action taking place on earth in the present day, and all of a sudden pigs start to fly, then maybe you should rethink. Drop some hints. Y'know.
4. It does the opposite of what it's supposed to. It's like putting makeup over a zit, but you only have your wintertime concealer and you just spent two weeks tanning in Hawaii. It pulls the reader out of the action and says "Hey! You see what I did there? Wasn't it weird? Weren't you kind of uncomfortable with that?" And then the reader says "Yeah, it's like you're in a novel - a bad novel." Even if they were prepared to accept whatever you've just done, they now have been slapped in the face with it and their feelings are hurt. It is non-preferable to hurt your reader's feelings.