Anyone know

#1 The quick and dirty way is to RMB-click on your geometry and select Geometry > Delete History. This will delete your active node and remove all the nodes before it. The active node is locked and the geometry is now part of your scene. You cannot make changes to parameters on that node anymore and unlocking it will leave you with nothing (although you can undo the unlock).

The other approach that I often use is to select a large chain of nodes and simply put them into a subnet (Shift-c in the network view). This hides the nodes from view and then I can give them a label like "body" or "right arm." You would be surprised how useful it can be to go back and work with the nodes from "before."

Once I was modeling an airplane and I suddenly noticed that a fuse I did on the front of the plane ended up fusing a bunch of windows together. I had spent a number of steps working on the nose since then and didn't want to lose that work. What I was able to do was to go back to when the windows were fine, select the back part of the plane and create a copy node. I then went to the end of the chain and created another copy for the front of the plane using the end of the chain. I then merged and fused these two parts to get back in business. It would have been hours of work if I had deleted the history.

#2 That delete history was exactly what I was looking for, I always save a backup before I do something like the delete history so if I did find a screw up I wouldn't have to go back too far.