A truly sour taste causes abundant salivation, at least in my case. It's not out of pleasure, it's more like a forced reaction, like my glands are trying to drown out the taste. This doesn't mean it's a bad taste, I actually had a girlfriend who enjoyed pickles a lot more than chocolate, and a friend who would drink unsweetened lemon juice like a boss, right out of the bottle...
I have an idea to describe it... Have you ever licked a 9V battery, just to see how it feels? Well, the sensory overload in that case seems mechanical to me, like your tongue is seizing, like a muscle spasm. Sour is the chemical equivalent of that. It can make tears shoot out of your eyes and sometimes make your whole body spasm and spaz out, much like getting a slight electric shock. It's also very acidic, astringent. Usually sweet&sour or simply sour foods don't go that far though.
I don't know if that's the case for you, but sometimes dry red wine makes your mouth sort-of pucker up. In Romanian we call this "a-ti face gura punga", which loosely translates to "turning your mouth into a bag", in the sense that it tightens it up. This doesn't happen because the wine is sour, it's a different reaction to a different chemical (tannin), but I'd say it's precisely at the threshold between bitter and sour. If you've ever experienced that sensation, than sour taste is similar, except much more potent.
By means of synesthesia, I'd associate sour with the color green, with the touch of something raspy, like a cat's tongue, with the sound of sparks sizzling as they fall into water, the C# musical scale...
I'm about at my descriptive limit, lest I start really turning poetic. Hope this helps!
Smilie, or it is an acquired taste like "meaty" or "fishy" and can't be described.
