Synesthesia is estimated to effect up to three percent of the population. People experince it in many different ways, including seeing sounds and smells. I have the most common form, color-letter synesthesia. It is not detrimental, and actually helps me remember things. When I used to work at the airport in catering I could remember what gates and planes that I have visited by the colors I assciated with them.

Synaesthetes tend to confuse left and right, which applies to me. Although I am excellent at navigating and remembering spatial directions, when giving directions to people I confuse left and right all the time.

A correlation between the artists and synaesthetes exists, perhaps indiacting that people with synesthesia are more creative. I am not sure if this applies to me.

Here are some Synesthetic links:

Synesthesia: Phenomenology And Neuropsychology
A review of current knowledge of synesthesia. – The author mentions that synesthetics are good at remembering the spatial locations of objects including memorizing floor plans and maps. This is a skill that I have. Also, he mentions that they often have right-left confusion (which I often do).

The UK Synaesthesia Association
This page provides a lot of great background info on Synesthesia.

Trends in colored letter synesthesia
The type of synesthesia that I have is colored letter synesthesia. This paper seeks to identify trends among several synthetics and their colored alphabets. My alphabet matches the trends pretty well.