At the moment, I love my CAE, but that was not always the case, and I expect it could change again in the future.
When I bought him, I knew there were two very similar fish - one good (SAE) and one bad (CAE), but I really couldn't tell the two apart in a fish store, and was told the one I was buying was "the good one". (Blame the minimum wage lfs employee or myself for not being better educated about a livestock purchase, even if he was only a couple of dollars?)
Anyway, I was looking for an algae eater/ bottom feeder for a 10 gallon tank, and was told he'd be great for the job. He was great at first... cleaned up my very minor algae problem in no time flat and seemed very appreciative of the little cave I'd made him. But, in time, he got bigger, and as he got bigger, he got meaner. This is when I educated myself a little better about the difference between a SAE and CAE, and realised I had, in fact, purchased 'the bad one'. Eventually, he was swimming up to slowly moving fishes and sucking onto their sides. Anybody who looked weak was eaten. I didn't know what to do with him.
I decided to give him one more chance in my new 45 gallon tank. I was prepared to remove him and take him to the lfs if things didn't work out, but thought it was worth a try. I have silver dollars in there... the perfect fish to suck onto (just ask my yo yo loaches). The CAE has been perfectly behaved, going on two months now. He's always very busy cleaning and exploring, and even seems to be behaving quite socially, often seen shoaling or resting with my cories. I have seen veil tailed fish swim right up to him and my opaline gourami chased him away from a fern he wanted to nibble at... no reaction from the CAE. He's roughly 5" right now (doesn't stay still long enough to get a better guess or real measurement). I know he may double that size, and if he does, I expect that he'll outgrow his current environment and probably start acting very nasty again. Hopefully, I'll have a bigger tank he can move into by then; if not, lfs for him, I guess.
So, to answer Anna's question, I do think they have an unfair bad rap. It would be like putting an Oscar in a tank of guppies and then complaining about his behaviour. Or, less radically, it's not unlike putting five male guppies with one female. Chances are, they'll pester and mate her to death. That doesn't mean guppies are mean or bad fish, just means you didn't provide them with an appropriate environment. I hope I can continue to successfully house my CAE; he's an attractive, active fish with a lot of personality.