ZOMG! Could this place get any more crowded? I only go there when I absolutely have to. Do your research apriori, go in and get out as fast as you can.
I have been to other locations in the US and in Europe and this one by far is the least zen.
I've gone here a few times to meet with them Genius Bar folks. I don't mind the delay even after making an appointment; sorta inevitable like waiting at the doctor's. However, I do mind the bedlam surrounding me while waiting for the delay. It's a total barn house.
The Genius Bar guys have been consistently superb. One interaction stands out: I went in around 5 pm on a Sunday to get my top case replaced and since I was on a deadline, Harry turned it around for me in 30 mins, even though it was close to closing! He also told me that apparently top cases on the macbooks are replaceable for free up to 5 years after initial purchase! Phew! since I've already replaced mine a few times and my extended warranty has long demised. Harry also picked up on the funkiness of my missing serial number and rectified it.
The staff here seem to have a handle on the crowds, but I've always had to stalk someone and then pounce the moment he/she becomes free to help me with my non genius bar questions. It's pretty Darwinian in there!