Just got back from the prerelease, and I'm happy to report that I did fucking awesome. Got my first 4-0 at a prerelease, losing only one game in total and getting 1st place overall (apparently the 2nd place finisher had one more game loss than I did).

The format is basically: you choose your main guild, then get a guild pack from that guild, plus one from a guild that shares a color with yours (but not from the same set). For instance, I went with Simic (Gatecrash), and was paired with Golgari (Return to Ravnica). You also get 4 packs of Dragon's Maze in addition to the guild packs.

For those who aren't familiar with some of these new cards, just search for 'em here if you're interested:
http://gatherer.wizards.com/Pages/Default.aspx

My guild packs were fairly underwhelming (the rares being Biomass Mutation and Underworld Connections), but my Dragon's Maze cards were far more promising. Got Advent of the Wurm and Scion of Vitu-Ghazi (neither of which I used), plus Zhur-Taa Ancient, and a Ruric Thar and a foil Varolz in the last pack. I also opened enough good removal, card draw, and mana fixing to make a Jund deck (Red/Black/Green), with some Blue. I broke the golden rule by having a deck with more than 40 cards, but I think my results justify my choice.

Decklist
Creatures (13)
1 Kraul Warrior
2 Zhur-Taa Druid (These things are nasty. Mana ramp and pinging all in one cheap package)
1 Sewer Shambler
1 Battering Krasis
1 Stonefare Crocodile (Runner up for MVP, interestingly. Lifelink saved my ass in at least two games. In one case, this thing let me come back to win after being down 22 to 2.)
1 Drakewing Krasis
1 Varolz, the Scar-Striped (Didn't come out often, but his Scavenge ability helped fuel a few wins, including the all-important last game. Never ended up needing to regenerate him, interestingly.)
2 Korozda Gorgon
1 Zhur-Taa Ancient (Worked nicely, but led to my only loss. This big dumb brute let my opponent fire of a Debt to the Deathless for 20 to finish me off.)
1 Sapphire Drake
1 Ruric Thar, the Unbowed (MVP. Hit me a couple times, but I won every game I got him out save for one, and even then he still burned the opponent for 12. Might make room for him in my Mayael the Anima EDH deck.)

Instants (5)
1 Biomass Mutation
2 Putrefy
1 Turn/Burn (Only ended up using the Turn half once. Still proved quite useful in several games.
1 Far/Away

Sorceries (4)
2 Pilfered Plans
1 Urban Evolution
1 Armed/Dangerous (This baby is a game ender. I wouldn't have won the last game needed to go 4-0 without topdecking this with a Korozda Gorgon on my board and 5 untapped creatures on my opponent's side. +1+1/Double Strike/Must be blocked is devastating on a Deathtoucher. :3)

Enchantments (2)
1 Stab Wound
1 Gruul War Chant

Artifacts (3)
1 Dimir Cluestone
1 Rakdos Cluestone
1 Golgari Cluestone

Lands (19)
2 Island
4 Mountain
5 Forest
3 Swamp
1 Dimir Guildgate
1 Simic Guildgate
2 Golgari Guildgate
1 Transguild Promenade

For my victory, I got 12 booster packs of Dragon's Maze. That's 1/3 of a booster box, so not a bad haul by any stretch of the imagination. The rares I got were:
Ready/Willing
Flesh/Blood
Catch/Release
Notion Thief (Foil. This thing's worth 15 dollars. Might do some inquiring to see if it's likely to go up, then sell it if not.)
Sire of Insanity
Render Silent
Godless Shrine (lands have their own separate slot in this set, so you can get a normal rare with a rare land)
Advent of the Wurm
Varolz, Scar-Striped (nonfoil)
Mirko Vosk, Mind Drinker
Vorel of the Hull Clade (One of the cards I wanted from this set for my Prime Speaker Zegana EDH)
Plasm Capture (Ditto.)
Blood Baron of Vizkopa (Cool creature, not in my colors. Worth 11 bucks though, so I'll probably trade it off or sell it posthaste.)
Ral Zarek (Whoop whoop. Don't know if I'll keep this. Might just sell it for mad ducats, as it doesn't look like a good fit for my Niv-Mizzet EDH)