I've seen a few posts on the other site about how terrible weapon trip is. From what I understand, it's a one-round lag for the victim and a one-round lag for the tripper. Is that about right? Or is it two-round lag for the tripper? If the latter, I guess I can understand the complaints.

That weapon trip edge that saps moves seems handy though, no?

I found it pretty weak. Partly because it seemed like you couldn't trip translucent or wraithformed people, which is a large percentage of the "people I can't trip the old fashioned way" category. Plus the lag was pretty lame, even when cheap shot fired. If I'm fighting a guy solo and he's convulsing then I could weapon trip, but I might actually be better off fleeing and trying to knife him. If I'm ganging a guy I can't trip and I'm not tanking, then I'm probably better off circle stabbing.

Plus, with thieves, everything has an opportunity cost. If you spend four points on weapon trip then that's four points you can't spend on something else. If you have four points to spare and nothing else you think would be useful, then go ahead and take weapon trip.