One of the new aspects of the new MM DevNet is a new location for user-supplied tips, with categories for all the MM products. Pretty nifty. I don't recall seeing this on the old DesDev site, so if it's not really new, let me just point it out for those to whom it IS new. :-) It's at http://www.macromedia.com/cfusion/tipsubmission/main.cfm. There are links there for all the products, a highlight of both the "highest rated" tips and the newest tips, and of course a place to enter your own tips. As for that "rating" feature, you can rate a tip when you view it. It may not be obvious, but you mouse over the stars that show the "average rating" and on clicking a star, you're giving it at that rating.
While you're on that page, take note of the separate "tip of the week" link, which takes you to a page with a large number of video tips. These quicktime videos walk through using various features in a variety of MM products. These have been around for a while, though many may have never seen them. Check 'em out!