To get back on track, UK has had a couple, but not really for football reasons:

4* QB Drew Barker - Not disappointing for on-the-field reasons, because he redshirted last season behind Pat Towles. However, he was the face of the 2014 recruiting class and then was charged with running around shooting airsoft guns at three other players and then involved in a bar fight in Richmond just a few months later. He still has plenty of time to turn it around, but is probably walking on eggshells right now.

3* RB Khalid Thomas - A pretty exciting Florida RB/WR prospect who (along with his brother, LB Pancho Thomas) was caught smoking weed and eating mushrooms at the Arboretum by Lexington cops. Both of them were dismissed from the team. Thomas never ever made it to fall camp, but was dismissed in July '13, just a few days after arriving.

3* RB Justin Taylor - Was offered a greyshirt at Alabama, which was the Kentucky standard of greatness under Joker Phillips. He was awful every time I saw him in open practices. No idea what happened to him, he was a pretty highly regarded recruit but his balance was awful and he was always tripping over his own feet. He ended up transferring to South Carolina State where he rushed for 937 yards and 10 TDs in the last two seasons combined.

Those are the only guys I can think of from the last three recruiting classes that have seen the field.