I picked up a filter to protect my new 12-40mm f/2.8 lens. That big front element looked very unprotected. (Read the review conclusion here.)
Filters are a strangely controversial topic on gearhead forums. Many gearheads go crazy at the idea of putting a filter in front of their lens.
I have found these B+W Digital MRC Nano XS-Pro filters to be the best at not causing any ghost reflections when there are bright lights in the frame.
Why do the marketing people put the word “Digital” in the name? Are they not allowed to be used with film cameras?