I knit most of my socks on 2 circulars, one sock at a time. Working on both socks at the same time would require me to carry around 2 seperate balls of yarn and could get too bulky for my purse. But, I can understand why people suffering from SSS (Second Sock Syndrom) would want to give this a try!
Wildsky -- One year I made a pair of those slippers for every member of my family for Christmas. I was SOOOO sick of the pattern afterwards that it took me another year to get around to making a pair for myself! They are wonderfully warm, but do need to get thrown in the washer and shrunk back down every once in a while. As people wear them, they tend to get a bit bigger.
I did use the leather soles on the bottoms, but I've also heard of people using the puffy paint that is used to paint designs on sweatshirts and such. You can get it at any craft store. Also, I saw another type of slipper bottom recently at a yarn store in Michigan. They were cloth with non-skid stuff on them; they reminded me of the bottoms of the old fashioned footed PJs we wore when we were kids. If you can find those, they may work better for you and I'm sure are less expensive than the leather.
Oh! and I've heard of people using old purses purchased at second hand stores for the leather, too. Obviously, it would take a sharp knife and steady hand to cut up a purse to make slipper soles.