I'm so tempted by this, wish they would tell me when the sale was over so I'd know how long to procastinate.
According to one of the threads in the Steam forums this may only be good until tomorrow, the 14th. They link to this image
as proof. If people are on the fence and haven't acted yet, you may want to act soon.
I picked it up. It's a fun non-stressful distraction so far.