While this forum has low activity, I'm gonna share some of my thoughts/tricks/bugs - let's keep it in one place for once. I suggest you may post your tricks/bugs/ideas and I will insert them in this post (with credits of course) - so it will be kind of material where you might find something interesting. I'll keep this updated and I'll do some screenshots when needed (I thouhgt about videos, but for now my pc is not good enough, but I'll give it a try).
These two are, in my opinion, most gamebreaking glitches and I use them all the time (well, it's kinda cheating, but it's how game works):
1. Double power usage
Activate power, then right click to use it - and immediately press it's hotkey - when you're fast enough (that is, before you use it/power does damage, so you might not use it when close to your character - that way you can press hotkey before he fires) , you should be able to shoot twice (usable with any aimed power). Be careful, I noticed that when using thunderous shot, your second use must be targeting terrain, NOT monster - if you target monster, you will get nothing. Also, with Icicle Blast you have to be fast(er), so it's better for you to aim far away - that way you have time to press again hotkey, before you get there and shoot.
2. Animation break glitch (!!!)
Idea is - you can shoot MUCH faster when you break animation with stop command, or move command. For example - you cast Grasping Vine, and normally after cast, your character makes nice moves with his hands - but if you press STOP hotkey (or move) - it breaks animation and you can cast it again! It works with EVERYTHING - even with melee fighters - but I don't think you need it that badly. This glitch works best with crossbow and slow spells - but even if you improve your speed slightly, it's always something. Also, quickened casting just shrinks the time of animation, so it takes less time from attack command to spell being cast - I didn't test it, but I think with this talent maxed and grasping vines, using this bug speed would be awesome.
Earlier I thought it's good only for solo play, because stop command stops every party member, regardless of party order. But then I discovered that move command doesn't stop you. You only move somewhere else, which doesn't affect other party members. I have move command bound to 'x' key and it works wonders (for ranged/casters - melee fighters have to position themselves all the time). So i just hold down right mouse button on enemy all the time, and just after I cast/shoot, I press 'x' immediately and I shoot again. By pressing 'x', my character moves only a little bit towards enemy, so it's not a big deal (you can do that by stop command with party in mirror mode, when everyone has the same attack speed). That way you can have party and still take advantage of this glitch. It's the most awesome gamebreaking stuff (crossbow wielder with this and double thunderous shot (glitch 1) can blaze through the game easily.