Oh, I love talking about this. (overlong post)
I just have grapheme-color and a bit of sound -> touch* and color synesthesia. Usually I just associate instead of projecting, but rarely I project right into my normal field of vision (more common when I'm upset and in memories). Listening to music in the dark can be really fun with this. I really wish I could draw the things I see, but they always elude me and I can hardly draw anyway. They would make nice desktop wallpaper.
My visual sense of time is boring. I see weeks as a straight line, and an year is either a line or an arc pointing upward depending on how I am thinking about it. (Going over years without getting too specific produces arcs.)
I used to share number-personality synesthesia with my sister, but we both grew out of it. For example, for me 6 was jealous and manipulative and 3 was playful and innocent.
For me synesthesia is never a problem except when I'm having severe migraines**, though that could be something else entirely. I don't have visual migraine auras, but when I'm having really bad pain from migraines I see the pain as big white flashes that impede my vision. Mostly it helps me as a memory aid. In particular, grapheme-color synesthesia was useful during Mandarin Chinese class for memorizing characters. (I didn't use any formal methods for connecting characters with colors, and didn't know at the time that they existed.)
*This kind of synesthesia is normal in a mild form, right? Some tones are "warm" or "smooth", others (often reverbed or mostly high-frequency) are "cold", some are "chunky" etc. I also think that it is influenced by the tactile experience of playing instruments, but of course it also happens listening to crazy generated noises that don't sound like earthly instruments. Synesthesia as a normal and cultural phenomenon is fascinating.
**Seeing as migraines are also neurological phenomena and sometimes involve random sensory disturbances (the auras are seizures, I think, and also appear in epilepsy), could they be related at all? Perhaps causing temporary synesthesia, or just correlated with it?