Booked the appointment online, Went in at the correct time, one of the staff in the store told me "Spoke the people in the back of the store with iPads, they handle genius bar appointments, Spoke to them (took my name), quickly found me in the system and told me they were very busy atm I could wait or rebook (It was lunch time in a city centre), Said I'll wait, Told me to take a seat over there --->, said "tell them to give me a shout as I'm hard of hearing" (Am a little but not too bad, I just wanted to waste my time playing on a mac instead of just sitting at a full table twiddling my thumbs (dead battery on my phone, didn't think about bring my charger with me), told the person "telling the system I'm here" this they laughed and said OK.
10-20ish mins later (Lost track of time, was dicking about on the net), someone shouts my name, got his attention and we went to a quieter table (guess the hard of hearing thing worked :-P). Docked my phone and started running some tests, while running the tests we talked about Work, games (A nice discussion on which was our fav build of Counter Strike).
Yup I needed a new battery, Would take 60-90 mins to replace. Agreed to the repair terms (Yes I took a back up, no I will not sue if you have to wipe my phone, Yes you may claim my first born, etc etc etc). Told them I had ID (They wanted a method to make sure that I was me when picking up my phone, asked "what if I didn't have my ID on me as I don't normally carry it?", said they have other methods they can use like showing the same Credit/Debit Card I used to to book in the job.
Went and got some food, went to visit one of my fav bars in the city centre, went back about 90 mins later and spoke to the same people at the back of the store who had the iPads. They said "all done, someone will be with you soon" 5 mins later I had my phone back with a new battery (showed my id to say I am me).
Apart from the genius bar being busy (Would be nice if I didn't have to wait, but a) I knew I booked a lunch time slot b) I made "plans" not to do anything that afternoon. So not the end of the world for me. But I could see it being a pain in the ass if someone was trying to drop their device off during their lunch break and had to wait around.) I can't say that I had a bad time there.
Store in question if it makes a difference to anyone: New St Apple Store, Birmingham, UK.