I may have got this wrong but I'm sure I read that Sigma are doing a HSM version of this lens for Nikon... but I didnt read about Canon.
Will a Canon version follow?
Do Sigma tend to make Nikon mount lenses first?
I'm also sure it said something about 18-50 getting HSM again for Nikon.
And I found this info after googling and cant recall the site it was on, sorry