I dunno why it won't sort the items based on the new dates OP plugged in. That might be worthy of sending the creators a comment if it doesn't straighten up and fly right.
I mainly use Ravelry for patterns, too, and I've also inputted all my knitting and crochet books and magazines in the library. This is particularly helpful for the e-mags that I have. I include notes for each e-magazine about the patterns I like; then I don't have to sort through three year's worth of publications (which is tedious when you have to open every one and scroll to the projects page).
I also discovered not too long ago that when I "search by patterns in library," it will include patterns from the e-mags, too (and as long as someone has uploaded an image of the project--original or otherwise--I can see a picture of it). This also keeps me from having to open every PDF version.
I've used Ravelry to look up a specific yarn and see what kinds of projects people have made with it. Reading their notes can give me an idea if a yarn has a nice drape or if it's difficult to work with or whatever.
I'm sure Ravelry has lots of other great uses; I just haven't figured them out yet!