I agree with Mr Skills, buying in John Lewis is a good idea, the staff however don't know what they are talking about though, In southampton I was listening to what the staff were saying to the customers, i.e. I can't seem to install iPhoto etc from the Tiger install disks I bought in here. The staff said they will be there just explore the disk. and other stuff like that.
Micro Akita on in london are very good, Well in my experience the one in the basement at selfridges are the best, they seem to know a lot about Macs and are not as busy!
PC World as well, DON'T BUY coverplan! Believe me I used to work at currys and then PC World! It is Cr@p! buy Applecare for your new Laptop direct from apple if you want to extend the warranty.
Harrods in knightsbridge - Again they seem okay, they don't seem to keep that up to date though, back in July they still had panther running on their machines!
If i were you, Buy from an Apple store! I know I will for my next Mac!