Now keep in mind this is still a good amount of money for most "regular" films....but considering the budget of SUPERMAN RETURNS and past 4th of July movies a $16 million Friday night gross on its first weekend in release is nothing spectacular at all. If you assume it's going to gross just over $50 million (maybe less?) on the three days of its proper opening weekend (on over 4000 screens too), that has to be a bit of a disappointment.
Or look at it this way: it opened Tuesday night, and won't cross the $100 million mark until quite possibly a FULL WEEK later. You drag a heavily-hyped movie like this out on 4000+ screens and it takes that long...well it's not the sign of the apocalypse but it certainly means Superman is no Spider-Man at the same time

It probably has something to do with the movie and lack of word of mouth....In fact, I'm guessing it will be quickly forgotten by the time PIRATES 2 rolls out next weekend, and probably will have a tough time grossing X-MEN 3 numbers if it does a fast fade. It's certainly the kind of film (slow pacing, lack of action) that might have a problem generating word of mouth (and again I didn't hate it but I was definitely disappointed).
1. SUPERMAN RETURNS WARNER BROS. 3,915 16,210,000 4,140 n/a 48,268,444
2. DEVIL WEARS PRADA, THE 20TH CENTURY FOX 2,847 9,479,000 3,329 n/a 9,479,000
3. CLICK PARAMOUNT 3,749 6,235,000 1,663 n/a 64,752,522
4. CARS BUENA VISTA 3,706 4,038,000 1,090 n/a 172,059,783
5. NACHO LIBRE PARAMOUNT 3,082 1,812,000 588 n/a 60,585,173
6. LAKE HOUSE, THE WARNER BROS. 2,645 1,433,000 542 n/a 35,725,472
7. FAST AND THE FURIOUS, THE: TOKYO DRIFT UNIVERSAL 2,666 1,345,000 505 n/a 48,215,240
8. WAIST DEEP FOCUS FEATURES 1,006 1,010,000 1,004 n/a 12,859,180
9. BREAK-UP, THE UNIVERSA 1,906 869,000 456 n/a 108,134,000
10. DA VINCI CODE, THE SONY 1,384 650,000 470 n/a 208,142,832