That's one of the strategies with the group bombs. I'm the current holder of that bomb at .39BTC. When it levels I'll make a profit of .1BTC. It will cost me .2BTC to buy out the level (if no-one else joins), putting me at a new liability of .1BTC (down from .39). It it reaches the next level without my intervention I'll get back an additional .05BTC, putting me at a total gain of .15BTC while limiting my total liability throughout the process. It can be complex to keep up with it, but as long as there is any interest with the group bombs it's not too difficult to make a profit. Obviously the easiest way is to invest and then have someone else scoop up the entire next level.. but where's the fun in sitting back and watching.
Aaaah, that makes a lot of sense. It seems like everything is now a group bomb...is it always like that?
Not initially, the bombs almost always start off as single user bombs, if they go a certain amount of time with no buyers most of them seem to turn automatically into group bombs (and the clock restarts <-- very cool).