i have twice used the apple genius bar at the covent garden apple store and i am very impressed with the service i got. The first time was due to my apple tv would not do mirroring on my HD tv, but everything else worked, like streaming youtube / bbc iplayer from the phone or iPad to HD tv via the apple tv. so i booked an appointment and went there with my apple tv, and when tested it worked perfectly, the mirroring that is so the apple tv was not at fault. so the guy suspected that it was my net gear router from my broadband service provider and he was right, cause i took the router next day and in the apple store it it would not do mirroring. on the 2nd day with the router i just walked up to him without appointment but he still helped me out. after some tinkering with the settings which didn't help he suggested that i get a better router or get the airport express, which i did much later on and i have mirroring now works. but i was happy that the apple tv was not at fault, just the cheap router.
second time i went to the same place was when i got my mac book pro and it double registered me with the iTunes in one account name and not in the other. booked an appointment cause i was not familiar with the mac computer settings as it was new to me, the genius bar gentleman merged the accounts with me and explained me how the settings worked, he also showed me the short cuts and trackpad gestures which was great help. also because i was a windoze user, he help me with the mac equivalent of how to use shortcuts for copy/paste.print screen. all in all it was good experience and the waiting times in both instances was not long