I think the most important thing everyone needs to know is that every function members get for free on DU2 will also be free on DU3 (if the function exists at all on DU3). Plus, we have also created a bunch of new functionality that will be available to everyone, regardless of whether you purchase a star membership. For example, we have a new "My Subscriptions" function which gives members the ability to subscribe to their favorite small forums and easily see when new threads are posted in any of them.
As I said in
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=439x2300356">my post, those who choose not to purchase a star will still be able to post and participate free of charge.
I think the biggest thing people will get on DU3, in exchange for purchasing a star membership, is that they will be be able to view DU without seeing the ads. There are a number of other things that star members will get, but they are all related to new DU3 functionality, and I don't think it would make much sense if I tried to explain it here. For one thing, star members are given more opportunities to help run the site, by serving as hosts in our big forums, by helping to keep the site clear of trolls (to name a couple things).
But I think it's worth noting that at this point we are not asking anyone to sign up for a DU3 Star Membership at the full rate. Indeed, you will not be able to do so until we move into DU3. The point being: You won't have to decide whether the features and functions are "worth it" until we have already moved into DU3 and everyone knows exactly what they will get. For now, all anyone really needs to know in order to decide whether to donate is whether it's worth a few bucks to surf DU without ads for a year. Which is all you've ever needed to know in order to donate to DU.