Actually, there are just a few places today where you can still meet a geisha on the street, the best known being, of course, the old Kyoto district of Gion. In Tokyo, I saw geisha inside the Senso-ji Temple from Asakusa and I know that many of them are also working in Akasaka...
They are usually very camera-shy and I think that's very understandable, considering the amount of tourists assaulting them with flashes, especially in Kyoto...
But that's not always the case - one day, visiting the Keisei Nippori Station to assist at the inauguration of the new Keisei Skyliner AE train, I found myself face to face with a couple of friendly geisha - actually they were maiko (geisha in training) or more accurate hangyoku (the word used in Tokyo, maiko is a Kyoto term) - present here for the same festivities.
One of them caught my gaze, I smiled and showed her my camera and she smiled back, posing for me as I took a few photos. Unfortunately they were on the other platform, so I was able to thank her only with a bow and another smile...
EXIF info:
Nikon D90
Lens: VR 18-55mm F/3.5-5.6G
Focal Length: 55mm
Aperture: F/5.6
Shutter Speed: 1/320s
ISO Sensitivity: ISO 200