The demo happened today and was a blast. I used these forces:
Orks:
[340] "Normal" Ork Warband w/6 Boyz, 2 Nobz, 2 Grots, 4 Battlewagons
[340] "Normal" Ork Warband w/6 Boyz, 2 Nobz, 2 Grots, 4 Battlewagons
[150] 6 Stormboyz
[225] 3 Stompas
1055
Marines;
[300] 6 Tac units with 3 Rhinos
[300] 6 Tac units with 3 Rhinos
[175] 4 Assault units
[300*] 3 Whirlwinds
*fudged, only allowed 3 Whirlwinds
I set up and laid the trap, prepared to snare who I could:

It wasnt long before I had caught a pair! A father-and-son pair stepped up and really enjoyed the game:

Able to sneak in front of the lens once, here I am instructing on some of the finer points of Epic to the pair:

My lovely assistant, Bryan, who kindly provided the painted demo units, steps in here to teach when I called away at work to...*gasp* work...

Bryan, getting dividends from the karma of providing the awesome models, gets in a full-scale game with someone who had heard of the demo beforehand and brought a Space Marine force to battle with:

All in all, I felt this was very successful. We played the basic training mission of grabbing a single objective in the middle. The first demo pair went with a lot of sustaining fire actions, and only really had one Assault, at my urging. The Warbands really shot up the Marines in this one. Game two, which was me and another dedicated onlooker, was much bloodier because I explained the "Double tap" to the player, and also introduced support fire during assaults. He played well but I inadvertently smooshed him when he assaulted one of my formations that was solidly supported by 2 others...and I showed him how support fire
really worked

Nonetheless, he was hooked.
We also had a lot of people who knew about it, had played it, etc etc, so we got the word out quite a bit.
Such happy times down at the FLGS!