Originally Posted by
orca15
I read it as 250MQM for registering, and double bonus miles after that.
That's my read as well.
Sign up for this offer and you'll earn 250 Medallion Qualification Miles (MQM's) to elevate your Medallion status.
Plus earn double miles and get to Award Travel faster when you book and complete a two-night stay between now and December 15, 2012 at any participating hotel or resort within the Hilton Worldwide portfolio.*
It also looks like you don't get MQMs for additional nights, it's simply 250 MQMs and done.
Update: I actually agree with Ascii that the fine print overrides the email wording, and you probably don't get miles just for signing up but do get MQMs for doing the 2 night stays, which does, ultimately, make more sense.