I love ravelry too! I have been a member for 9 years! I joined shortly after they opened, back when there was a 1-2 month waiting list for invitations, and have used the site consistently ever since. I definitely see some similarities although I think ravelry's scope is much larger (millions of users and pages, full database functionality, and pattern sales) so it does not feel quite as intimate and friendly as ylf to me.
Actually at some point I thought about starting a ylf ravelry group but didn't think there would be enough interest....
ETA: the article's point about ravelry having great user retention is true, although I stay/participate for different reasons than I do on Ylf. For me ravelry fulfills some really knitting-specific important functions - the pattern database and my personal project notebook/record are the main ones - whereas I am on ylf because I honestly love you all. (I love talking about fashion too but if the people weren't nice I would just read the blog and stay away from the forum).
Both rav and ylf are also really well-designed and user-friendly sites, which is a huge part in getting people to come back. I think I've mentioned this before but Casey, the webmaster behind ravelry, basically built it from the ground up by himself, and I honestly think it's one of the best designed sites on the internet.
