Well, Mocha never forgets anything that involves food. If she saw me throw an apple core in the woods at noontime, the second I let her out the door hours later, she'd make a beeline right for it.
Other than that, I think she's actually turned totally disobedient in the last year or so. She just does exactly as she pleases now, and to me that's kind of funny -- just like a crotchety old lady!! She seems to be selectively deaf, and seems to get quite a kick out of ignoring me when she doesn't feel like doing what she knows she's supposed to.
Hershey, my current senior, doesn't seem to have any memory problems and he must be 15-16 by now. And I don't recall my first YF having any problems with her memory.
My second YF, however, was diagnosed with Cognitive Dysfunction Syndrome (sometimes called doggie Alzheimer's) when she was about 13. It seemed to me that was more confusion than forgettfulness per se. For example, I would ask "Do you want to go out?" and she would run to door but she'd have her nose at the hinge side rather than the opening side. Or she would get "stuck" halfway though doorways or behind furniture. Weird stuff! My vet eventually prescribed selegiline (Anipryl) for her. She took it for her last year and it virtually eliminated her CDS symptoms.