Last fall I cast on for my first ever toe-up sock, the Discovery Sock from Cat Bordhi's Personal Footprints for Insouciant Sock Knitters. The method is intriguing: in a nutshell, to make a sock for yourself, you make a cardboard tracing of your foot. The measurements and stitch counts you record on that foot serve as your pattern after after for that particular yarn and needle size. Essentially, you knit a tube for your foot and cut into the ankle line to create an "afterthought leg."
I cast on my toe stitches and increased to the number that fit over my toenails comfortably.
Then I tried on the sock as I knit and increased sole stitches whenever the sock felt tight. When I got to the ankle bone -- or the leg line as Cat Bordhi calls it -- I threaded two lifelines in and started on the heel decreases.
Then OMG, with moral support from Yvonne, we put the lifeline stitches back on the circular needles and cut and unraveled the stitches in between, leaving an opening for the leg.