Looks like it is underperforming to expectations.
http://www.boxofficeprophets.com/column/index.cfm?columnID=9696
It turns out that BOP was over-optimistic on the opening weekend prospects of the long-discussed Snakes on a Plane. Steve Mason had projected that the movie would earn $39-42 million in its first three days, while Reagen Sulewski had forecast $44 million. Both analysts were banking on the fact that the Internet buzz had been roaring almost from the moment the film's title was announced. The question, though, was always whether that type of fanboy buzz could truly translate to great August box office like horror predecessors Alien vs. Predator and Freddy vs. Jason. Apparently, if you don't have a "vs." in your title, $40+ million is not in the cards. Ordinarily, BOP eschews tracking numbers, which can give a good general sense of awareness and potential, but oftentimes will miss certain breakout films. This week, however, trackiing was closer than we were, although it was slightly low. Snakes on a Plane earned $7.8 million on Friday, a number that does include late-night Thursday showings totalling $1.5 million. As far as the weekend goes, Snakes on a Plane will suffer both from being in the horror genre and from having fanboys that rushed out to see it on Friday. A 2.5 Friday-to-Sunday multiplier would be quite in line with expectations, which would give the Samuel L. Jackson film $17.3 million for the weekend. We're disappointed that more animals-eating-people fans didn't give this more of a shot, particularly since it's even Fresh at RottenTomatoes.