I just started a Shadowrun game so I actually had to answer this one as of late. It varies on my goals for the game - if I'm looking at a fast short story arc, I'll put the PCs together by hook or by crook and start off somewhere fun. It seems the intro varies by the estimated length in the long run.
For example, a one shot or convention game, everyone walks in knowing what they're doing from the game intro. They've got a mission lined up already and they just start in media res. For example :
You all work for a company called ACME Inc. You aren't runners - you deliver items *for* runners. If they need a pair of rocket propelled rollerskates delivered out to I90 by tommorrow - you're on it. Which is good - cause guess what you're doing tomorrow morning...
Vs. a short campaign. I'll have some good excuse for them to all be together but the players won't know to start with. I try to guide character creation, or set up the game so it won't matter if they're all from different walks of life. I will have some challenge up front to get them all on the same road within one session though. For example:
You all wake up - you don't remember how you got here. You hear the echos of gunfire around you. You are dressed in a uniform you don't recognize and there's about 30 corpses on the ground in this room also dressed in the same uniform. You see six others in the same uniform in the room. No one else is wearing any other kind of uniform. Oh.... and all of you have a gun in your hand.
Result: John Woo at the table in under 5 seconds. Really amusing as they talked themselves down from killing each other. But they formed a 'where *are* we' style party in under five minutes.
Lastly, a long campaign. That one I take characters and try to note any characters too far out of line before the game. Loners make great movie characters - and *horrible* RP characters. I'd rather have Ocean's 11 than Punisher. Heck - I'll even take Reservoir Dogs over Punisher. Tweak contacts up front, interview players up front to make sure we're all wanting the same sort of game. Then... toss the characters up in the air and see where it lands. Since my players are all on the same page, my characters aren't automatically against each other and I've done my social engineering in advance... it'll fall into place like dominoes.
Usually I open with a 5 to 30 minute intro for each player held in private, it gives them a chance to stretch into the character and me some experience with the player/character without outside influence. That's their plot hook for getting into the game - I'm given to understand from one of my players this is unusual but incredibly effective.
Once they're all set on course - we start gaming all at the table and see where it goes. I tend to prefer teams for long games that form together in an organic/natural way - it lends towards stronger RP later on because there's a real reason for the characters to be together. For my current sort of players it lets them feel much more in control of the circumstances, and like they are the stars of the story.
My current Shadowrun game, the one just started - is on game 3 - the team hasn't formed yet, but is well on it's way to it. Players are having a *blast* (which is the point after all), and they've at least gotten to groups of two so far, last game ended with two PCs in the back trunks of two *other* PCs cars... I'm suspecting that another PC will soon be making the rounds to call and hire some runners (*cough* the other PCs will be at the top of that list most likely) to go steal some art back... so barring any player coming up with something truly unexpected - I'll have a formed run team within 2 game sessions.
Then I can start having the bad guy stalk them.
