Haven't been in a property that had a tip jar. I guess I'm a bit mixed on this. On the one hand, if they really go out of their way then you want to help. On the other it seems a bit tacky to have a jar or plate out. I'm also pretty self-serve.
What I have done, however, is write the GM & Bill Marriott re: great exec lounge staff, mentioning them by name, saying how great they are, and asking that my letter be put in their personnel file. I know in 2 properties for staff that I've done this that the GM has made sure they know about the letter, either by providing a copy of it (one showed it to me on a subsequent stay) or posting it on an internal bulletin boad, or bringing it up in a meeting. I have no idea if they got pay raises or incentives, but I know the GMs appreciated their efforts/the kudos.
Cheers.