to create a selection set simply select the nodes you want to live in that set, run the SelectionSets proc and give the new set a name.
This will make a "SelectionSets" menu visible that can be used to quickly select a predefined group of nodes.
Also a group of controls for each selection set is created in the script's settings panel to manage the set (i.e. select, deactivate, add or remove nodes from the set, etc)
There are a couple of redraw issues when creating the menu (if anyone knows a way around that please let me know):
After the first set is created you have to hover your mouse pointer to the right of the last menu entry in the menu bar to force a redraw of the gui. The new menu will magically appear.
After saving and reopening a script that contains selection sets you'll need to go to the scripts settings panel again and hit the "update menu" button in the new menu tab (this runs the updateMenuScript.tcl).
Now hover your mouse pointer over the empty space in the menu bar (see above) and you should be set.
Couldn't find a way to automate this but you will only have to do it once per session.
example menu.tcl entry:
menu "Other/@B15;create selection set" SelectionSets