Since bspinner asked (and my sister is begging for one), here is what I can tell off of my Friday addled brain:
I have used Sugar n' Cream worst weight yarn, doubled, on #10 needles, mostly because I haven't bothered to get #10.5, which would make the knitting more comfortable. I think I will continue to use the #10 needles because I suspect the tightness of the gauge makes the mat a little stronger. I knit using Garter Stitch. The original pattern calls for seed stitch, but I like the cushiness of garter stitch.
The first two mats I knit are 2 colors (2 balls of each color) and checkered. If you have more tolerance for many balls of yarn flying around than I, you can use intarsia. I myself knit 3 strips, 23 stitches each. Knit the first color until relatively square, add the second color and knit that for the same number of rows, repeat the first color. You'll want 2 of these strips, and one in which the colors are reversed. Sew up the strips and Voila! Bathmat!
The balls of Sugar n' Cream I had seemed to be extra large, and I managed to get most of the way to a second mat. This time I just knit 2 rows of each color. It's almost square and I didn't have quite enough yarn to cast off (I cheated, don't tell).