Mathematical abilities and spatial navigation are below average. There has been quite a bit of research done on the superior memory abilities noted in people with synesthesia. The most famous case is that described by A.R. Luria in The Mind of a Mnemonist based on his studies of a Russian man referred to as S. in the book. S. had synesthesia to a greater degree than is common, having associations between four senses- sight, sound, taste, and touch, and thus represents an extreme case. The Good, The Bad, and The Intriguing I will describe S.'s attributes in order to show the greatest extent synesthesia is known to influence someone's life.
Most people have fewer and scaled down characteristics.
The problems that S. and other synesthetes have to deal with are often different then those of people without synesthesia. This seems to be a fairly common experience of people with synesthesia. It can be seen as wonderful because everyday experiences can be much more intense and emotional but it is also possible for it to get in the way. Also, it seems to inhibit concentration in some cases. The same ideas apply when reading.