reasons for long crank

What are all the most common reasons for a longer crank when starting a car? I just noticed after servicing my air filter that it cranks longer than usual.

Poor fuel delivery due to bad fuel filters, worn out pump, minor leakage, or gunked up injectors.
Or poor air flow due to an air filter in need of replacement, but since you just did yours, I would check to make sure it's the right filter for your car.
The only other reason I can think of is temperature. If it's really cold outside (like below freezing) and your car has been sitting in that for 8+ hours, it's perfectly normal that you have to crank the starter for longer. Although In Albuquerque, I doubt that's the issue.