Who will he ride for?
Well I seriously doubt he'll ride for anyone but Astana. Which thickens the plot. Alberto Contrador is the best stage racer in the world. He's already said that if he rides the tour next year he's going for the win (regardless of whether Armstrong is on his team or not). We might be looking at a less intense version of Hinault and Lemond. Lance will ride for Astana, do you think Trek would allow him to ride for another team?
Why is he coming back?
Lots of people seem to doubt his return being spurred on by promoting cancer awareness. While I think that's a part of it, I think Lance's return is primarily due to his ultra competiveness. I think getting beat by Wiens lit the fire within. Remember that Armstrong didn't loose much in cycling. He missed the competition.
How good will he be?
It's Lance Armstrong. He's not going to be bad. As you get older you don't necesarily drop off in fitness it's recovery time that suffers a bit. That said I don't think Armstrong has aged enough to really be effected. He knows what it takes to get his body ready. He's won the Tour de Georgia but he's never won the Tour of California. I think he steals the show from Levi in Cali, and wins won more tour with Bruyneel.
Is it good for the sport?
Yes. I love the Velonews web article that interviewed all the US Directors. They seemed super hesitant to say it's good for the sport. Well that's because they don't want to get robbed of America's crown jewels (Tour of Cali, Georgia, and France). With amazing Tour de Frances by Columbia and Slipstream they are finally gaining solid fanship in the states. Now Lance comes back and puts them on the back burner.
For fans like us this will be awesome. It's like Jordan coming back from baseball and winning more championships (sorry 1996 Sonics). You know he's going to win, it's just a matter of how.