I'm using a protector that was included with my case. Based on the record so far, it should last a good long while, but I'm easy on things.
I do cringe at the thought of the people who pay $15 (or more!) for two sheets of plastic film at the Apple Store or other places, and then complain that they can't install them without bubbles. It's not that hard...
Let's face it, the whole iPod accessories ecosystem is a huge racket with inflated margins. Injection molded plastic, cables, films, and power adapters sold at many times what they cost, even with indirect costs factored in. Then there are the ultra-expensive headphones with very liberal warranty replacement policies; uhh, guess what, they probably couldn't afford to just send brand new replacements for every frayed cord if the costs weren't factored into the pricing.
I tried to succumb with only a case because it provide genuine utility in different ways.