I just spent a half hour narrowing down a bug in an application I’d fut some polishing touches on in PHP5. When it was moved onto the production server earlier, it came up with blank pages. I wasn’t on hand to check it out, so couldn’t help over the phone. I had to wait until I could get to a computer to debug it.
The end problem was in a line similar to the following:
$n=$db->query('select id from some_table')->numRows();
The above worked in every server I had available – except the one it was supposed to go on.
To get that code working in PHP4, you must break the object results down:
$n=$db->query('select id from some_table');
$n=$n->numRows();
It’s an annoyance – but at least it’s not a large thing to fix, and the lines that need changing can easily be found by grepping for numRows().

Interesting. Is lack of backwards compatibility going to be one of PHP5’s features?
It’s the other way around, hostyle – I was writing code for PHP5, but the code didn’t work in PHP4. No biggie – it’s a small difference, but I was suprised by it anyway, as I had not come across any other differences up until then.
ah yes, speed reading does let me down now and then