I have been using other packages for quite a while, one of them is Archicad…get around line modelling is so fast, not because I have used it for a long time but you simply learn 1 set of gestures ie to trim a line you simply hold ctrl and click on the segment of any line (or any linear element), To split linear elements into segments, you multi select and ctrl click on the cutting object and voila…since 87
Am I missing something…I couldnt see anything about gesturing in the forum or docs? I cant tell you how cumbersome it is…unless Im missing it which I would humbly apologise 
In Rhino, Ctrl and Shift are used to add or substract from a selection.
You can use any shortcut however to assign to the functions you mentioned. The default for trim for example is Ctrl+T, but you can also assign this to an alias or function key. Does that help?
Thanks for the reply
Thats also the case but its a bit more sophisticated in that certain areas of objects will display a cursor to denote target etc. Shift is still used as multi select but I think you would have to use it to get it…its actually so natural and I havent found anyone implement it in other packages which is a shame as its so good.