I generally like them.
It at least used to be a fresh approach and when done right, it gives you a kind of immersion and believability that's different from other movies.
If [REC] would've been made in a traditional style, it would've been a fairly by-the-numbers horror movie with a limited setting. But thanks to the first-person-perspective of the camera, it's one of the scariest movies i know.
Paranormal Activity was very enjoyable because it was unpredictable and goes against the usual horror film pacing, adding more uneasiness with each scene because you know it's gonna get worse, but you don't know how.
Unfortunately, it became the new "Once-a-Year-Horror-Franchise".
Strangely, i never liked Blair Witch Project. I found the characters horrible and overly hysterical. Last few minutes were fun, but the rest was just annoying.
There's a lot of crap with found footage movies, but it's the same with every other genre and subgenre, especially Horror.
That said, soon there will be a time when Found Footage cannot really offer something new unless it does something dramatic and very different (i'd like to see a live action, contemporary version of FLAG, aka a First-Person-Film about a War Reporter)