Thanks for bringing this up, Sam. It's a good question.
RebelPrincess pretty well nailed the explanation as far as that goes. If you're in the regular forum view, the topics are listed in reverse order by whatever topic has received the most recent comments. When the topic is blue, it means there are replies you haven't read; when they're gray, there's been nothing new posted since the last time you looked. And indeed, "sticky" topics are just topics that will remain pinned to the top of the forum, usually because they're important. But, for instance, I ought to unstick that sample mix, since by now everyone can see how to post a mix. :D
The interface isn't as linear as AotM was, I'll admit. It's a lot more dynamic in that the most recent stuff is given top billing. However, there are a few points that we should consider.
Like Barry, I'm not a fan of the 'bump' posts. However, I also know that we're all fans of our mixes and want people to see them! Alas, the functionality of the site comes down to how visitors interact with the site.
One thing I can't stress enough is that you can click on any member, and it takes you to a page called "(mixer name)'s Blog", which is a total misnomer because it isn't really a blog; it's actually one page that shows all their posts on the site. So by clicking on, say, Sammy's blog, I can go back and see all the mixes he's posted among all the comments he's made. It's a handy thing for looking back at people's older mixes.
Now that I have the ability to set up subforums within forum topics, I briefly considered setting up a separate subforum for each mixer. But I sort of rejected that pretty quickly; we've already got 39 members, and that list of subforums would quickly become unwieldy.
But if you want to keep your mixes in one place, I encourage anyone to start a single thread that you will regularly post to, and just post all of your mixes on that single topic. So then instead of having ten different threads for ten different mixes, you can have just the one overarching topic called "Billy Bob Thornton's Mixes" or whatever, with each mix showing up as a single post in that thread. The only limitation there is if someone winds up wanting to post a comment about a mix you made three mixes back; it'd just show up in-line on the thread.
Another handy thing that you may not have noticed. If you look up on the top of the sidebar, where it says Recent Posts? If you click on "See More", you get a page that shows every post on the forum in reverse chronological order. Handy?
Also, in the main forum view (when on http://mixtapes.lefora.com/forum/) you can see two blue buttons at the bottom of the white part of the page. Clicking the first shows all the topics in reverse chronology, regardless of what section the topic was started in (The Mixes, Music and Mixing Talk, etc.). The "Newest Posts" takes you to the same page as that "See More" I mentioned above.
There may be more things I can do, and ways to organize and make this more functional. I'm still digging around. Any suggestions are definitely appreciated!