I don't use filters, even if I have a lot expensive, large-lensed (is that a word) SLR glass. I never actually managed to get "cleaning marks" on my lenses and the only lens I ever dropped ended up having a blocked AF gear but no damage whatsoever was done to the glass. Also, I have some lenses i bought with scratches for absolute bargain prices. It's the kind of scratches you have to carfully look for, but they are there, and I never noticed any impact on the images taken with them, even if I had the opportunity to test against unscratched identical ones. I have the firm belief, that putting filter in front of your lenses will increase flare problems more, than any small scratch or cleaning mark can.
And since damaging Lenses isn't that easy in the first place (go, get a defect worthless lens off ebay and try to scratch it... The only object in our houshold, that worked was a quarz crystal) I think my lenses are well protected by their hoods. Of course there are situations where a filter makes sense, like when it's very sandy (beach etc.) or the lenses don't have modern robust coatings. So when there is a special reason why a lens would need additional protection, then I'd put a Filter on it. But not all the time, that seems paranoid to me.