I cannot tell you how many times over the years that I have read don't put a cheap UV filter on a good lens. I have taken many thousands of pictures and never bothered taking my filter off to see if it made a difference. Well today I did and all I can say is WOW, what a difference it made. I bought a Nikon 70-300VR lens with a UV filter when I purchased my Nikon D90 and have never been too happy with the pictures it took. Well today I removed it and wish I had done this a year ago. There is a noticeable improvement with it off. This picture was taken at 300mm which is where all the reviews said that it was soft. I still haven't perfected being able to post a sharp picture on the forums but even so I don't think this one looks too bad.
Please do yourself a BIG favor and remove your filter and see if it makes a difference for you as well. I am MUCH HAPPIER with this lens now, Jeff