Using UV filters on the front of lenses is the biggest con, ever.
You're effectively adding another layer of glass to however many layers of glass are already in the lens. It's another cause for internal reflections. Most of them are cheap pieces of junk to begin with.
Don't worry about getting your lenses dirty. They can be wiped clean. I've had my L-series lenses out at the beach, under thundering waterfalls, deep in forests, and they've managed to survive without a scratch. You just have to be sensible. The lenses were meant to be used. Don't let a cheap filter adversely affect your images. Never used one, never will.
If you're really concerned, just leave a good quality polariser on the front -- at least a polariser makes a visible difference to your images. I don't use them for people photography.
Greg, I can't comment on cheap polarisers as I've never used them. I've always felt that I have good gear, and, it should be treated with good accessories. It does not make sense to me to skimp out on accessories when I've already spent thousands on the rest of the kit.
The Hoya Pro1D is multicoated, to reduce reflections, and has a slight warming effect which I like. It means I don't need to add saturation in post. I let it all be done in camera.
These are just things that work for /me/. Other people's mileage may vary.
H