There is a new thing starting called Ravelry that sounds interesting. Lickety knit has a good description. The bit that sounds the coolest to me is:
“And a pattern in your project queue is automatically linked to all the other people who have made that project and information about the substitute yarns they used.”
This of course will only be useful if other people knit the same pattern and those people are in the subset that heavy users of the web related to knitting and that people actually post.