Gridding is not cheating at all in fact Rembrandt used a huge grid in front of his models to achieve better proportion its far more accurate and saves time rectifying mistakes made from guesswork. I hope this helps.
Can you specify what sort of proportions you're referring to? Sighting and using grids are excellent ways to maintain proportions, especially in still-life/landscape drawings.
If you're drawing people, proportions may be more easily accomplished by using the proportion rules of the human body. For example, when standing straight with your arms at your sides, the elbow will be at the same level of the belly button. The body will also be approximately 7 heads tall etc.
I've started using grids, even for drawing people, and I'm starting to like it. I thought that gridding will take away the flow you have when you draw freely, but it doesn't. It's even better because now I'm not wrestling to get the proportions right. Thanks so much :)