There's going to be as much debate about filters as there is
over film vs digital. Short answer is, everything has its place.
I got a cheap Tiffen UV for my general-zoom when I got my first
(d)SLR. After a few months and a few tests, I got rid of it. I
could actually see the difference that it made to lower IQ (not
only the vignetting at the wide end). But then a few years
later, I got the new Canon EF 70-300L, and put on a B+W MRC
filter. Testing and pixel peeping with and without, there is
absolutely no difference to IQ. Not only is it better glass, but
it's multicoated (unlike the cheaper ones), and it's easier to
clean with some fancy coating.  Sure, lens hoods protect against
falls, but lens hoods also tend to prohibit using CPLs (in
general, but I hear Pentax makes a nice one with a cutout). And
lens hoods just won't protect against sandblasting. Maybe you
don't go down to the beach and shoot surfers, but I do. It's
dusty and windy and sandy here in Aus. So if I'm going to shoot
surfers or birds on the