I have finished having two of my books reviewed by Smashwords and have had them both accepted into the Smashwords Premium Catalogue. It's a great day for me!
What makes this so exciting? Well… if you are an 'indie' (independent, self-published author) on Smashwords, then you WANT to be included in the Premium Catalogue. Being there gets your books distributed to many more places: Apple's iBookstore (32 countries), Barnes & Noble, Kobo (multiple countries), the Diesel eBook Store, and Baker & Taylor (Blio.com store and Axis360 service for public libraries). As they add more retail agreements to their repertoire, your books get out to more potential customers. More potential customers means more people get to see your books means more potential sales. So, being accepted into the Premium Catalogue is a very good thing for me.
How does one get into the Premium Catalogue? It isn't all that difficult, really. The thing you need to do, after writing a terrific story with fabulous characters and making certain that your grammar and spelling seen to, is to get the formatting done right. To do that, you download the free "Smashwords Style Guide", written by Mark Coker, founder of Smashwords and follow it implicitly. If you do this, you will get into the Premium Catalogue. If not, you probably won't.
There is a good article and information about the Premium Catalogue at http://www.smashwords.com/distribution. You can also download the Smashwords Style Guide from there.
Good Luck! And may you gather many, many fans. :)