It took me a while to get into Ravelry, but now I'm finding it more seductive in the time-wasting department than even my Bloglines feeds.
It has a fantastic database that allows for all kinds of searches: by yarn weight, by pattern type, by just-about-any-search-term-you-can-come-up-with. You can read reivews of yarns before you buy them and find out which are evil and pill almost instantly or that split while you knit and drive you to distraction. And the pattern galleries have helped me make some decisions--you can see what the sweater looks like on real bodies, read about alterations people made, and find out if the pattern was well-written or made people swear a blue-streak.
Thanks to Ravelry, I have FINALLY found a pattern to use up my huge stash of Rowan Biggy Print Yarn:
Unlike many sweaters made with superbulky yarn, the people wearing the resulting sweaters in the Ravelry gallery did not look like they were drowning in wool. I have a tendency to get claustrophobic in bulky yarn sweaters and feel like I'm being swallowed up by a not-entirely-friendly sheep who wants its coat back.
I'm still searching through the Ravelry database for something to do with all the Swish Worsted yarn that I bought to make a wrap sweater (got 3/4 of the way done and realized that I look like I'm wearing a bathrobe when I wear wrap sweaters and ripped it out). I might divvy up the yarn and make this gathered pullover for me and some sort of sweater for Fiona who has commented lately on my selfishness as a knitter.