Spence,
Drysuits change everything... Your muscles stay operational longer... And operational muscles are just kind of important when you're kiting/sailing... Yeah, I used to where a drysuit even in warm months in colder water and it would add a couple of hours atleast to my sessions, and they were more effective sessions because I didn't care one bit about falling in...
Since my drysuit more or less gave up the ghost (actually had a couple pinholes, but it was still perfectly operational, I just couldn't get myself to replace the seals again, the colors were 1990!) after having it for 13 good years (replacing the seals 4 times) I've used a full wetsuit which has surprised me as to how warm it is, but I will probably be getting another drysuit here pretty soon. I did actually buy an O'neil Boost a couple years ago and didn't keep it because the seals aren't covered by other material like my OS Systems drysuit's seals were for UV protec. I think the OR's are really good that way.
If you go with a breathable (Gore Tex type material) they are very expensive. But you don't sweat. I remember sailing at Grantsville in November with my drysuit...
As to the limits of temperature to which Marty was referring, I've concluded that 48 degrees (at least that's what PVU read) is the limit to comfortable riding... Anything below 48 degrees is going to result in some serious pain! Forehead, fingers, feet... Really fingers are the most painful part... But I have some new neoprene gloves, a 7 mil hoody and I'm going to test that limit again this year once I get my drysuit.
http://www.ossystems.com For a comparison... There is a Kiters Drysuit for sail at WindWing in Hood River... It has some killer features. I didn't buy it because it has a neoprene hip seal dividing torso from legs which seemed wierd to me. But the guy selling it (new/used) would probably take $150. (large)