There is no 'set' level of what's deemed desirable... however, the RDA was miscalculated, and adults should be taking closer to 10 000 IU daily (certainly not 2 000 IU) :
The serum levels differ in how they are measured. Commonly, most frequently used descriptions will be in ng and nmol.
USA uses ng, while Europe commonly uses nmol measurements.
I'd go with Vitamin D council recommendations:
So, I'd aim for a level between about 80 to 100 ng - which can be achieved by taking about 20 000 IU per day... however, I think you can safely increase and stick to 10 000 IU for yourself.
Also, it is recommended to use Vitamin K2 MK-7 (100 to 200 mcg every 2 days) in combination with Vitamin D.
I found that combining Zinc Picolinate of 50 mg daily works great with the above (especially for the skin).
However, in order to not necessarily overdo things... just stick with Vitamin D3 10 000 IU daily and K2 MK-7 200mcg every other day.
The best thing to do is to have your blood level checked -- vitamin D 25-OH, (not vitamin D 1,25). In the USA the labs consider a normal range to be between 30 and 100. In my experience that 30 level is still a bit low. People feel better when their levels hit about 50. I've written a few things about this which you can find here: http://saynotostroke.com/?s=vitamin+d. You can't be certain of how much you should take every day without having an idea of what your level is.
Excerpt from the Vitamin D Society...
"The Scientists Call to D*action, a document published by a group of prominent vitamin D doctors, researchers and scientists, recommend that people achieve optimal vitamin D blood serum levels of between 100-150 nmol/L (Can) or 40-60 ng/ml (USA) for best overall health and disease prevention(3). Vitamin D deficiency has been associated with an increased risk for many serious diseases including bone disease, various cancers, infections, autoimmune diseases, cardiovascular diseases and adverse pregnancy outcomes."