I'm surprised, I guess, that it isn't going to do better, given that it's Shrek AND that it's in 3-D. It's getting a massive 3-D rollout (2,373 locations) and 3-D usually gives theater owners a license to rip off the customers. You would have thought the box office numbers for Friday would have been more inflated as a result. A theater in New York was reportedly going to charge $20 a ticket to gullible customers (a price that was later retracted -- it turns out the price was $19). It's obvious that customers aren't so gullible and that 3-D isn't the box office panacea everyone at the studios thinks it is. Quite frankly, people are downright bored with what they are getting at the theaters at the moment -- it's the same stale franchises over and over again. Based on this weekend, it is sooooo obvious that even the kids are bored these days with the movies.
Either that, or the prices are driving people away. Likely a bit of both.