My early thoughts.
The missions are posted to your global name and span across servers. You have a testing process in which you don't get any XP or drops, but you do get special testing badges (whoopie!). After testing (or not testing at all) you can publish your storyline. Published arcs give XP and drop something called "Tickets" which allow you to unlock more Architect options and also purchase special drops that you use to create Items. "Loot" if you will. After a character runs a published arc, a pop-up appears with 5 blank stars and an optional comment box.
The reality is that yes, people make PLing missions. So far nothing can stop that. Someone in my group has made the "ulimate PLing map" and I have to say it is insane! I'm sure it's a matter of time before nerfing happens. Of course there is a strong possiblilty for a mission like this to get large amounts of 5 star ratings. However, after publishing your arc, your story can become one of the "AE Dev Pick". This means that your mission will now grant XP and all the regular drops of a regular mission...actually a little better. It's pretty safe to say that the Devs will never pick a farming mission as a Dev's Choice. If Dev's Choice missions were selected by scoring alone, it would be a very different story.
Anywhoo...that's that for now. It is a very interesting concept that was well put out. It is not a perfect system, but when you are the first MMO to put out user-generated content, how can you expect that? It is very fun and adds a lot in terms of variety to the game.
I've been trying the Champions Online beta in the mean time and really can't wait for Star Wars: The Old Republic. This issue is doing a very good job of keeping my interest.