Reverse-grips require a "bump" on practically every set, due to the fact that the only filange keeping the weight from falling on your face, are your thumbs. That kinda sucks, since I really don't like to rely on other people too much, unless I am going heavier obviously(where it is a necessity), and asking for bumps at 205 just makes me feel unconfortable, and like a pest. Doing reverse-grips on the Smith-Machine was a good suggestion (as magman stated) since you only need to turn your wrists to unrack the bar, as opposed to having to lift it up & forward while using a freebar. You won't need as many lift-offs doing them that way. I'd have someone watching you just the same, in case you can't turn your wrists back to re-rack the weight. RG's could be dangerous for someone who has little experience in the gym due to the possibility of the weight slipping around the thumb, and coming down on someones head or throat. You really need to error on the side of caution while doing them, even if you know what you're doing. ALWAYS have a spotter!.
As far as overall effect, I like close-grips better myself. They are great for developing that long horse-shoe look. R-G's hit the other part of the tricep, from my experiences with them.