I would also say to look at
www.tfl.gov.uk (Transport for London) to look at the tube maps to see how easy it is to get to / from Mayfair should you stay outside of Mayfair. It also has a journey planner on there so you can put your start and end stops in and get an idea of the time it will take. Looks like Bond Street is the nearest tube station (on Jubilee and Central Lines) and is pretty central so fairly easy to get to from anywhere (there are lots of hotels in Kensington so you could go from Earls Court / Gloucester Road and then use Piccadilly and Jubilee lines to get to Bond Street).
Finally - another website to use is laterooms.com. it allows you to specify the area of London you wish to stay in.