Pal Mickey cost us $41.50 to purchase, as they gave us credit for the one-day rental value. As mentioned, he is triggered by certain things to make comments, such as when you near a certain pavillion in Epcot, he will tell interesting facts about the country, or when we got near the Tower of Terror in MGM he told us in no uncertain terms that he did not like T of T!
Also, he will play games, such as one where he will name an attraction and you will have to tell if it is in a particular park (by pressing his hand if yes, his tummy if no) or other yes/no type questions, such as if a particular character is a villain, or can fly. Many are for younger children, but some get fairly complicated and he is entertaining for adults, too.
He will "go to sleep" at times if you do not respond to him, which is nice. We didn't really have a problem with him annoying anyone, though, probably because the Disney designers have him shake a little and giggle if he wants to talk, but you have the option of ignoring him and he will be quiet, or of pressing his hand or tummy to find out what he wants to say. (Sometimes they are extremely corny jokes!)
He is fairly small, but a bit heavy due to the electronics. I thought we'd just rent to experience him and not buy, but my son really wanted him and after a day I saw that he was worth the purchase price to us, particularly if he is updated as planned, as we already have two more trips planned to WDW in the next few months.
Hope this helps!