While I always have an assortment of lubricants ready, I'm usually extremely wet.  For me, it's kind of a combination of things.... Of couse, how much I'm turned on would be part of it, but also, what time of the month it is... It I'm ovulating, then I get wetter, how much stress I'm under at the time... This can cause some problems.... And, what mood I'm in.  We all have days, hopefully less than other days, that we just don't want to think about sex and if I'm having one of those days, it's more difficult for me to be come wet.  Also, after an orgasm, most of the time, I dry up a little, especially if I squirt.  The strange thing about that is, though, that when I have an orgasm, I usually want more and more and more, so the lubricant usually become necessary!  Just my .02.  

Jaclyn

one other cause nobody has mentioned is if you are on any medication especialy an antihistamine that can also effect levels of wetness