Since I'm trying to pass my Master Knitter test, I figured I would do some test swatching to find out the truth about my gauge. I've suggested this technique to a few customers before and I decided to try it for myself. Make 2 swatches (in my case 3), cast on 12 stitches and knit every row or purl every row (I also knitted backward) for 24 rows, then bind off. The smaller the square, the tighter the knitting. This is what mine look like:

My square of backwards knitting is the tightest, followed by plain knitting, and the loosest by a long shot is purling. This would explain the mysterious "rowing out" on the wrong side of my stockinette fabric. I'm going to play around with more swatches until I get 2 that are the same size, so's I can become a master. My next step is to purl with extra finger wraps to see if that tightens me up a little.