I am a huge supporter of putting a high quality UV on the end of all my lenses. The last thing you want is for it to take even a little bump on the lens element.
Why? Apart from lenses like Canon's 50/1.4 that has AF so brittle it actually breaks from even a moderate thump to the front element, where is the danger? Particularly if you are using your lens hood as you always should?
Imagine it bumping onto the edge of a table slightly and gashing part of the coating off the lens, you will NOT be happy with the repair costs, trust me. Then let's talk about degradation in image quality with a lens flaw like that, self explanitory.
How is that self-explanatory? I'm ready to put a bet that it would be absolutely impossible to see any degradation because a small part of coating has been chipped from the front of a lens. And, again, with the proper Canon lens hood, your scenario is highly unlikely for most lenses.
When I bought my 5D in 2005, I bought filters for all my lenses but didn't use them with lens hoods. Later, after first real flare issues, I removed the UV filters one by one and started using lens hoods instead. Lens hoods are for protection, and unlike filters they actually
improve IQ. And, although I have zero front element scratches, I know that a few of them (would I be unlucky enough to get some) would have no effect whatsoever on IQ. Heck, even a cracked lens can be used! (See link below.)
http://www.lensrentals.com/news/2008.10.30/front-element-scratches
If you get a good quality filter, you will not see any appreciable loss in IQ of your pictures.
Except when you do. There are multiple documented cases where e.g. AF, IQ and strangely also bokeh of the 100-400 has been affected at the long end even when the highest quality filters have been used. Sometimes the differences have been dramatic.
I use Hoya Super Multi-Coated filters. If I have $1000s or more invested in each lens, it's not gonna kill me to put on a $50 filter to protect it.
It's not a question of cost, but of IQ and sense.m Why buy someting that at best doesn't degrade IQ much?
Besides, cleaning the lens elements constantly will wear the coating off the lens too.
Why would you clean the lens elements constantly? A small number of dust specks won't affect IQ one iota. I clean my front elements less often than once in a year and even then only when they have about half a gazillion dust specks on them. There has never been any appreciable before-after difference.
I still have the multicoated UV filters that I bought for my lenses. However, these days I only use them if I know I'm going to shoot in rain, dust, etc. Which happens only twice or thrice a year.
Kind regards,
--
And if a million more agree there ain't no great society
My obligatory gallery:
http://www.iki.fi/leopold/Photo/Galleria/ 
