I guess it really depends on how it's set up. I think most are set up so they only take pictures after the light turns red, so you'd have to enter on red to get a ticket. That seems reasonable, whereas entering on yellow should be allowed (or at least not subject to automated ticketing).
Biggest problem is when they start shortening the length of the yellow light in order to increase the number of tickets. I know this has happened in at least some places. That seems dangerous and wrong.
I've also heard of some cameras activating if you stop even a little past the line. You should always try to stop short of the line, but if you mess up and are a couple inches over that should not result in a ticket. Furthermore, if red light cameras become widespread, that means more people will be slamming their brakes and might wind up across the line despite trying to do the right thing. Especially if they're also shortening their yellow lights at the same time.
For a typical red light runner, though... I have no sympathy. I see way too many people run them blatantly, even entering the intersection after the light has turned green for cross traffic. It's worse for left turns; if it's really busy there will usually be one guy stuck in the intersection after the light turns red who has to go through late, but oftentimes there will be two or three people following and blatantly running the light and creating a dangerous situation. Fuck those people.