Well, 3M says it can be removed easily (using a hair dryer or hot air gun and simply peeling it off) and the installers and film retailers say the same, no matter how old the stuff is. Some anecdotal reports agree, though I think the film's been available for this use for just a few years. 3M has done accelerated life testing, but that's not a watertight guarantee.
I thought about this and eventually decided to use the stuff. Many dealers in this area are offering it on new vehicles, including exotic makes, and I thought the risk was reasonable. If I lived in an extremely hot/sunny climate and kept my vehicle outside, I might think differently. I'd probably just peel a test strip after a couple of years and reinstall, repeating every couple of years to check for damage or different fading.