Lots of trash talk going on here...
Sigma is facing a few problems with this lens, but so far I think they made the right decisions:
1) The EF 24-105's price is low, when purchased as a kit or as a used kit lens.
2) The EF 24-105's IQ is quite good.
1) The street price of this lens will soon be low enough to challenge the Canon.
2) Well, we will see
One thing to keep in mind:
Neither Sony nor Nikon offer lenses like this, so there might be a bigger market on the dark side.