Quote from Mama;422180:
One of my goals is to get one sharp and in flight, but that'd need a very fast shutterspeed and large aperture. maybe one day ;_;
You can do it. Try adjusting the ISO setting to a higher number. As you multiply that number by X, the time it takes to capture an image (with everything else being equal) is 1/X of the original time. In film cameras, this meant changing out the film being used (as ISO is a measure of how sensitive the film is to light), but it's quite easy to do with digital cameras. You'll suffer a bit of image quality at a certain point though, largely dependent on the size of the image sensor. However, don't worry too much, because I know the D90 has a much better image sensor than my "toy" camera, and I can get decent results up to somewhere around 400-800 ISO (though I prefer to shoot everything at 80 if possible).
Anyway, with a camera like that, there's no reason you shouldn't be able to take shot of a butterfly in flight (given enough daylight), even with a macro lens. Well, it might be challenging to focus on the butterfly, but otherwise it needn't be blurry.