I've used yatzr during recruiting for periods, and also haven't used it for periods of time (in fact, the only time I won NCs was when I wasn't using it). I don't consider it cheating, because I don't see it as dishonest or unfair. There's nothing on there I can't figure out by tons of clicks. Even the distance thing. You can easily use Google to find websites that will tell you straight line distance between towns.
I also know that there are people who play this game who are programmers, statisticians, mathematicians, etc., who have ways and means to individually and independently apply their special set of skills to win this game. Skills I don't have. Emotionally it feels like they're cheating, but rationally, they're not. Honestly, it's made me feel like quitting at times when I keep getting stomped by the same person who I know has the capability to crunch numbers like that. My spreadsheet skills are equivalent to my nunchuck skills, which aren't good, btw.
I agree with the others when they say it basically comes down to saving time. I don't see that as cheating. We all have different amounts of time to spend on this game. Some people are retired, unemployed, or have desk jobs which allow them to get their recruiting actions in. Some people have jobs where they can't access a computer for 8 or more hours a day. Some people have kids, too.
I believe the people who use yatzr would be just as successful without it. They just would play in less worlds (or none, it seems) due to time restrictions.