Oh, I can't resist the sock questions! Here are my thoughts:
Why make socks when you can buy them in bulk at the store?
For me knitting is more about process than product. Socks, like hats, are great fun to knit because compared to other knitted items they are quick to make, involve virtually no seaming and there is huge pleasure & satisfaction in seeing a complete, three-dimensional object 'grow' off the needles.
What is your favorite sock yarn?
There are so many but I might nominate a lovely cashmere blend that I had from Posh Yarn in the UK. The red dye comes off on my fingers but the yarn is so soft and luscious to work with.
What is your favorite online sock yarn store?
I've had quite a lot of things from Angel Yarns at http://www.angelyarns.com/ - very good for the Opal yarn range as well as their own hand-dyed, and I've already mentioned Posh Yarns for luxury blends: http://www.poshyarn.co.uk/
What is your favorite pattern from SKS?
I haven't made that many but I am slowly completing a pair of toe-up Beaded Rib socks (there's a nice photo in SKS, it's in the five-stitch-pattern section). I was on a steep learning curve with the provisional cast-on & hundreds of stitch markers on the heel and toe, but the beaded rib stitch pattern is lovely - not that hard to execute and looks really elaborate. I am nearly finished making these socks and I will proudly post a photo when they're done.