I have a cheapo vitacon uv filter attached to my lens when I just started out. Ever since I tried a B+W filter, I never went back to using cheap filters anymore. Swear by their quality, seriously. Cleaning also alot easier.
I believe that, if we can spend hundreds and thousands of dollars on lens, why not a little more just to protect our precious baby?
To that point, I have never invested in a lens where the front element is like a fisheye....feel too naked without a filter to protect it.... I heard of ways to protect fisheyes but not sure exactly how.