[math-fun] 1000s of rogue planets per star?

http://www.sciencedaily.com/releases/2012/05/120510100217.htm is a press release claiming our galaxy harbors 1000s of free-floating "rogue" planets for every star. I have not read the original paper (paywall) but this sounds very hard to believe. (Their theory is these planets formed soon after the big bang and constitute a lot of the "dark matter.") "The scientists calculate that such a planetary body would cross the inner solar system every 25 million years on the average." I'd like it if somebody were to tell me whether there is any actual evidence or is this pure theoretical speculation.