I think people are coming up with edge cases like "what if they helped you do something they weren't supposed to do, and complimenting them on it gets them fired?!", but that's an exception, and most people would use common sense and discretion in any reasonable scenario. As a rule, pass on a good word about people who help you, it's not that complicated.
My boss is great and part of that is being aware of everything that's going on. We're got some problem people who really love bypassing our support queue. And then some critical system goes down while their favorite developer is on vacation and we don't find out until they've escalated the problem to upper management.
If I got complimented by someone in another department for something he wasn't aware of, I will get asked for the context. If it's important, I need to create a support ticket to document it.
Personally, I'm fine with that but sometimes I really don't want to spend 15 minutes discussing and writing up what may have been a 30-second conversation.
