Like almost anything and everything (all together now, as has already been said); it depends how it's done. So I feel the same way about that device as I do any other.
A gaming blurring of the fourth wall that comes to mind is Spec Ops TL, with its use of load screens in particular. One of the points of that game was to eventually emphasise the medium itself and make you aware of your own engagement - and sense of responsibility/culpability - as it descended to its rather hellish conclusion. I'd had the WP scene spoiled for me before playing, but not the main twist, and no one mentioned how it used loading screens, so all in all that creeping break of the fourth wall was key to my incredibly strong reaction to it.
I know Deadpool's an obvious example, but I rather liked that some of his special moves in UMvC3 involved using the health bar as a weapon. Not particularly clever, of course, but a nice, character appropriate example of it being used well.
I particularly enjoy moments in films where the fourth wall's teased or played with, e.g. the tension that can arise when a character's eyeline meets the viewers'/camera lens, often at a key moment, at least thematically/contextually, and in a film where narrative conventions of eyelines within scenes are adhered to. There is a film I saw in the last few months that did that, but for the life of me I can't place it... I even remember mentioning it to somebody as I talked about the film.