Yes, that's opportunistic, and what I should have done was come up with a solid idea, THEN volunteered, and let the free convention pass come as a nice little extra. As it was, I was freaking out 2 days before the game about what I was going to run. Then it hit me: I'll steal the premise of "Reservoir Dogs."
Surprisingly, there were a bunch of people that signed up for it. I hear that some people even got turned away (which is unfortunate, because I was willing and able to exceed the arbitrary number of players I'd put on the form). The first thing I did was make everyone dice off to determine if they were the one that started the game with a bullet in their gut. I informed them that I'd be houseruling the damage system on that so there'd be a danger of them bleeding to death (other than the seconds-long time frame you get under the normal rules when your condition monitor fills up). I like the SR4 rules, but they don't simulate a conscious person going through the process of dying horrifically like the guy in the movie did.
Then I explained that they had been on a run, and it went down perfectly. But when they met Mr. Johnson, he handed them a bag with 20 million
in cash, which they all saw. Then the pigs raided the place, and Mr. Johnson took a bullet to the thinker, and half the team got wiped out. The PCs were the half of the team that escaped. When they got to their safehouse, a warehouse by the shore, they looked in the bag and noticed that there was only 10 million . I drew names out of a hat to determine who was the undercover that had sold them out. I did the same to see who had stolen the other 10 million . Long story short: the undercover and the guy with the gunshot wound just happened to end up being the same guy. The guy that stole the money used a pressure cannon to launch it at the Lone Star mobile command center as a distraction, but since I thought he was just trying to get it off himself before the rest of the group found it, I ruled that since it was a bundle, the rubber band holding it together held, and it just went in the hole they'd already made in the windshield, without anyone noticing (the command center was filled with smoke from a smoke grenade that had punched the hole in the windshield). One character stealthed his way away, while everyone else was drawing fire by running to a police boat that they'd emptied with MG fire. From there, they headed out to Puget Sound in a totally bitching boat chase scene, where the rigger made all sorts of awesome rolls, despite wound modifiers. That's right, it was the undercover, and he was delivering the runners to the cops. The runners didn't find this out until he used the police boat's water cannon to knock them all overboard, where they got to enjoy heavy stun modifiers. Only one of them had a swimming skill, and 2 of them were allergic to the water.
I was nervous GMing for outsiders. I mean, I GM all the time with my group, but they're my tribe, you know? If I was being a bad GM, I don't think they'd necessarily tell me unless it was really horrible, because they're my friends (and they know they probably couldn't do any better). They keep telling me I'm a great GM, but I've never been sure they weren't just trying not to hurt my feelings. So I was wondering if anyone at MARCON would be pissed that I was using some house rules (well, "me rules," since we weren't at anyone's house), and glossing over matrix stuff since I'm not so great at it yet in 4ed, etc. And one of the guys that got totally screwed when I let the rigger/cop blast everyone with the water cannon turns out to be an Origins GM (before this even happened, I was making an Origins character with cybergills, so it's going to look like I'm prepared for retribution). But I think everyone had a good time. They at least said they did, and this isn't a very friendly city, so if I messed up, I think they'd all let me know about it. I even had people that had been watching us play come up to me during the rest of the convention and get my contact info. So, while it was quite possibly the least original thing I've ever GM'd in Shadowrun, I think it did a good job of being different than your stereotypical "go here, get this" run, yet was still accessible for new players at a convention, and satisfied the SR veterans at the table as well.
There's not much of a point to this post other than bragging, though.
Not to mention being infantile, closed minded mouth-breathers sadly in need of some personal hygiene...maybe that's just the old days of working gaming retail in this town though coloring my perceptions. Except for the perception of smell, that was definately a bitter reality. 
I'll take cliquishness to preserve my nostrils though, thank you.
But what follows relates: