Mostly I do not use protection / UV filters because of cost and quality reasons.
I even don't use one when my little daughter is touching the lens during meal.
In cases with real harmful conditions (lets say photographing steel grinding) I use protective glases for me and for my camera :-)
Once I made a highspeed video of an assembling machine - very uncommon and unsave handheld because of space restrictions.
The lens was trapped in the machine - and the filter broke. But the lens was nearly unharmed.
Without filter the lens would not been trapped at the same point (because the filter was ~ 5 mm thick and jammed at the front) - but if I have moved a bit further and the lens would jammed and broke - and then I could not finish that job.
I have UV filters on all of my lens... i use B+W which are good quality!
I don't notice any effects the filter has on my photos, so no harm i guess... i occasionally get a window reflection, but i simply take off the filter...
I think they just serve a "piece of mind" that you're protecting your lens/investment... but like others already mentioned, they aren't "needed" unless sands blowing, etc.
I'm with the majority, I guess. I very rarely use a so-called "protection" filter. When I do, it's for extreme conditions such as the base of a waterfall (gritty spray) or maybe during an extreme dust storm.
I have several reasons for NOT using a filter. First reason is I've had a number of problems with them screwing up a shot, mostly because of flare or ghosting. Had several shots ruined that I was being paid to shoot. Second reason is I think a filter is just as likely to damage my lens as it is to protect it. I once had a lens fall "face" down, and the filter shattered. The shards of glass destroyed the front element. If had been using the lenscap instead, there wouldn't have been any damage. Third reason is it's actually cheaper for me to NOT use filters than to use one. To put high quality coated filters on all my lenses would actually cost me MORE than a repair would.
I use Nikon pro f2.8 zooms, and virtually never use a filter on them. I daily shoot outdoors in the very worst conditions that the Dakotas can throw at me. All of my lenses are perfect! Only had one problem, and was BECAUSE of the filter. I do use the lenscap, always, when not taking a shot. Lenscaps are FAR tougher than flimsey glass filter. I also use lens hoods. Those do two things. First, they deflect stuff from hitting the lens. Second, they absorb the blow and save the lens. All in all, I think the idea that a UV filter is going to protect much of anything to be wishful thinking. Just as apt to cause damage in my own experience.
gunfighter48 wrote:
I've used a protection filter on my lenses for over 35 years and it saved two lenses when I fell on ice. If I get into a flare situation then I take them off and shoot.
It would cost me a lot more to buy quality filters for every lens that I have owned the last 35 years, compared to repair those two lenses and especially if I gonna take the filters off every time I belived they could affect the image quality/ flare.
I'll admit - they do offer an ounce of protection for smudges or an accidental hit on the end of the lens. (maybe a couple ounces actually)
I've had several filters that have been smashed/broken when a camera has been set down too hard (fall, rapid change, baggage). But seeing as the lens is longer for the threads of the filter, would it have 'saved' the lens? I dunno.
The last filter that got broken, actually jammed the filter on the lens, taking a pair of pliers when i got back home to get off. Since then, I haven't bothered to use filters - mostly for cost and time to deal with them.
But also, when it comes to big primes that we use mostly: 200/1.8 (2 of them) and 400/2.8 - there is no option for front element filter: the hood works just fine
(as a matter of fact, one of my 200/1.8's took a serious hit last week when my shooter tripped - even with the only concern on the way down being the lens - the hood was bent, as well as the front rim had a massive dent in it - but all is fine with the glass)
I'm looking at my Canon 35mm f/2 with a 58mm to 77mm step ring on it right now. If you can't get or don't have a hood for your lens, I bet these rings would do a decent job protecting the front element.
modern lens coatings and sensors are at least as effective at UV filtering as a UV filter. i have too much invested in lenses to accept the degradation of using a filter when it's not needed.
Herb...
dlabrecque wrote:
Too much investment in lenses not to. Besides, landscape photography usually demands something to help reduce haze, whether it's a polarizer or a UV filter.
jhom wrote:
Save your money and use the hood. It probably provides more protection than any filter can.
+1
you know how careful you are with your gear. Have you put the front element of any of your lenses at risk? If so, how? the lens hood really does protect the front element...use it.
No protective filters, except for one lens that has one built in. Oddly enough, when I did a stupid and dropped the lens, the protective filter was fine but the front element got chipped. Go figure.
Use a filter when necessary to protect the lens or when you want the effect that a particular filter provides. When you do use a filter, use the best filter you can afford.
HerbChong wrote:
modern lens coatings and sensors are at least as effective at UV filtering as a UV filter. i have too much invested in lenses to accept the degradation of using a filter when it's not needed.
Herb...
Most DSLRs have a hot mirror directly in front of the image sensor that cuts most UV and most IR light, nullifying the necessity for a UV filter to cut UV light.
I used to use UV filters to make cleaning the front element easier. The problem is that after a while, the UV filters became more difficult to clean than the front element. Right now, my UV filters sit in a pile with my photography junk. Not really even worth protecting.
I always slap a high-quality filter on the front, and you'd be amazed at the crud it gets coated in on a regular basis... crud I'd otherwise be cleaning off the more delicate coating of the front element. You'd also be amazed at how dinged up the rings of some of my filters have become over the years.... dings that would otherwise be on the lens body, potentially affecting either resale value or lens longevity.
Some people talk about how dust, dirt etc. on the front element will not affect IQ.... well in that case how is a piece of multi-coated glass that lets 99% of available light through gonna affect the quality either?! Repeated cleaning of the front element will, however, potentially impact the coating at some point, which will affect IQ. At least that's how I justify using a filter
Still, it's a personal choice. Some use one, some don't. In my case it's probably more for peace of mind, which is a good enough reason IMO!
and especially if I gonna take the filters off every time I belived they could affect the image quality/ flare. 
- the hood was bent, as well as the front rim had a massive dent in it - but all is fine with the glass)