System training is pretty much all I do now. I haven't been able to go to the gym in a couple of months so I built a tiny wall in my basement. I have small(to first joint) edges, pinches, side pulls, underclings, and 2 finger pockets for little "system boulder problems". I work one arm lock offs with my feet high. I also like to place an okay hold with crappy feet and do BIG reaches to a not so good edge or pocket, this helps you with big moves and contact streangth.
With the little "system boulder problems" you try and do them as staticlly as you can. This helps you build up more streangth than if you were to do them dynamic.
I think bouldering in the gym has it's place though, it allows you do build more technique, where as system is more power. As I am lacking in technique I can't wait to get into the gym a few days a week now that cross-country is nearing its end.
I feel that system training is far superior to regular bouldering. I think the next thing I'm going to rig up is a campus board, but I think I need to get a little stronger before thats really worth it.