The event is described here (Facebook login required, but here is the relevant text) :
This is it, folks...the moment you've been waiting for.It's a virtual game, so all the prizes are virtual, too. I'm guessing that the "Benjee" is the online Bananagrams unit of currency for buying things in the virtual Bananagrams store. I do like the look of those trophy tiles!
You all have been practicing, so now it's time to show your stuff! The Bananagrams "Happy Monday" contest is a way for YOU, the players, to earn prizes and gain fame!
Here are the rules: Beat as many players as you can in Live Multiplayer games on Monday, July 6th, from 12:00am-5:00pm. That's it. Simple, right?
* GRAND PRIZE: 5,000 free Benjees and a set of elite TROPHY TILES (not available in the store).
* 2nd place: 2,500 free Benjees and 10 Charms.
* 3rd place: 1,000 free Benjees and 5 charms
* All top 25 players receive 250 Benjees and 3 charms.
The excitement begins on Monday, so start practicing and get ready to win! GOOD LUCK!
UPDATE: This has turned into a regular, weekly event.
LATER UPDATE: These online tournaments have ceased, but I'm leaving this up for historical purposes.