If the D90 is anything like the D70, I wouldn't worry much. I used the D70 for several years, and it was occasionally out of the camera bag in drizzle for several minutes, or under a dripping umbrella in heavier rain, sometimes getting a little water on the outside, and it never had a problem. I wouldn't leave it out unprotected in very heavy rain, however. A little water on the outside doesn't seem to be a problem, but significant water driving into it can cause problems (as I found out with my later D300 when it spent awhile in a tropical downpour in a partially unzipped camera bag - afterward, I opened the battery compartment and significant water poured out of it - it got very flaky for a few days but was a good as new after it completely dried out...).
Lisa
