I have seen the tip jar at a few properties and, like the others, I feel it is in poor taste. For me, the CL is mostly self-service and I really don't like the attendant hovering over me in an obsequious manner (the Omaha Marriott and the Renaissance Boca Raton come to mind), obviously fishing for tips.

Like Bigguy said, if the service has been truly outstanding or special requests were taken care of, an Abe or Ben thank-you card at the end of your stay would be appropriate.