Yeah I've found combinators handy, I didn't realise they were new to 3.0 though as thats the first version of Reason I've used.

I'm perhaps guilty of over using them, it's quite typical for me to use a combinator for everything, even sticking a single FX unit in a combinator, as it makes it much easier to plug in more fx later on if you feel like it. It also makes it easier to keep a track of whats what, as you can rename the combinators to keep a firmer idea in your head of whats what.

One of the things that will be handy when I start playing with it more is using a combinator to chain several effects together, then programming it so the combinator buttons map onto paramaters then syncing it up with Ableton live so I can control al the variance in the sound through a single MIDI channel mapped onto the programmed combinator, rather than having multiple MIDI channels mapped onto the various modules.