We started to collect such notes, they are usually on a chocolate box, on a business card, on a pretty note paper, so they are now all pinned down on whiteboard where other guest can see them. It makes a good conversation piece with new guests as well.
Sent them your review as well. Like a quick summery of your review of them, That might ignite the conversation for them to write you amazing review! I done this so many times. IT REALLY HELPS!