This is the shortest how-to ever, but for those of you (like me) who were on the fence about Impulses and if you could use them (or how to), here it is.
Make a new bus, add ReaVerb to it. In ReaVerb click Add under "Impulse Generation". Point it at a file/folder where your impulses are and pick one. The rest in that folder will show up in the dropdown.
Then just make a send for your tracks to that bus and voila, you can now scroll through impulses and see what moves you. Don't be afraid to try odd things, even if you mic your cab already. I'm getting some pretty neat results running a Cab sim'd AFX track into an Impulse. They all shape your tone one way or another, and you can come up with some pretty interesting tones.
Keep in mind that you can easily rename the VST instance so that you know what you're looking at, and to copy it to another track it's as easy as just dragging it to the bus you want to try it on.
I really like using them when recording a completely dry track using POD Farm (while monitoring with a patch), then reamping with a model, but instead of using POD Farm's speaker modeling, I'll use LA Convolver with a Red Wirez. Sounds much better than L6's own stuff.