It seems that the Sigma 50-150 f/2.8 EX DC OS HSM lens is delayed again. The lens was initially supposed to be announced in October, but according to an email from Sigma UK to a reader, the lens will not be released till 2012:
"The latest we have from Japan is that they will not be available until next year and Japan have not given us any dates. We apologize for the delay."
The Sigma 50-150 f/2.8 EX DC OS HSM lens was announced in February 2011. The price is still unknown.