I've been running a 7/8" ROH on older Jackson MKIV blades. I've gone up to 15/16" once, and liked it, but it does get a bit screwy stability wise even with waltz jumps. I generally prefer a bit shallow of a hollow, as you get better glide and "flow" I guess. But now that I'm moving onto jumps a little bit, I think I'll be going deeper, probably about to 3/4" or so whenever I get new blades. I tried shallower, because I met another guy who seemed about my weight/height, but was older, and he used 7/8, so I just went up and up, from 1/2", to 9/16", gradually up to 15/16" and stopped there. In general, though, I like it more shallower than most people, and I feel knowing that a shallower ROH and me agree more helped me a bit. Most people I know won't go over 5/8. I know back in "the old days" shallower ROHs were a lot more common, but now people seem to prefer deeper. I think partially it could be due to my weight, I'm a guy and 195lbs, and so I think a shallower hollow suits me better.
So, what radius do people here like using?
I'm on 3/8".. I may be in the minority that prefer a deeper hollow. I skated on 3/8" in my old phantom specials (which were dovetailed) and was used to a MUCH more aggressive bite angle than I am skating on with the same hollow on my paramounts... I could actually tell the difference when I switched blades. I'm used to it now, but at first I felt like I was skidding constantly.
I skated on 1/2 for a while, but I switched blades and now I have them between 1/2 and 7/16. Our sharpener recommends going with a shallower (rather than deeper) hollow, so you can develop proper body lean and pressure on the edge (according to him).
You might want to take a look at the recent "ROH for Beginners" thread, too: http://skatingforums.com/index.php/topic,3691.0.html
I use 7/16" and will never again go shallower. I used to get 1/2".
7/16" pretty much exclusively.