Personally speaking I don't mind if someone uses my tree. After all I got a huge amount of help from a tree a relative of mine, now sadly no longer with us, did before me. Without him I doubt I'd be where I am in my research today. Also, for me, huge breakthroughs have come from requests I've made for help here at Rootschat. I suppose I'm coming from a place of feeling like my tree isn't all my own work, so sharing is fine.
I'm nervous about someone using my original research because I'm a beginner. I know at times my tree contained errors, which I've tried to iron out, but I wouldn't want someone to copy the errors.
I do look at other peoples public trees online on Ancestry. I can't say I've ever taken much information from them, as usually nobody has info that I don't already have. I've always assumed however that as their trees were public they didn't mind sharing.
As a whole I really enjoy sharing the things I have found and I'm working on a website which will host my results.
I'm not sure how I would feel if I became aware someone had borrowed my whole tree. If they really belong in the tree I think I'd be pleased because it's nice to share the information. If they did it in error and attached it to themselves in error I think my view would probably be more fool them.