Having not used any filters for a very long time I made the leap and bought an upscale ring for my camera so that my old filters would fit. Things have moved on since I last used them...we now have digital files instead of film and we have software that just about creates any kind of filter effect you could wish for. I still went out and gave it a go though. A few really just did not work but the graduated sepia one made some quite good effects, as did the graduated blue one.
The problem with the filters is you have to make the decision to either take all your gear out with you on the off chance you will use it or decide beforehand what you are certain you are going to use. My photography expeditions really aren't that thought out usually!