I switched from stock Debian Squeeze php 5.3.x to dotdeb’s 5.3.10 yesterday on a lot of servers. Usually a minor upgrade shouldn’t introduce any major changes, but in this particular case I’ve come across several customers having encoding problems. It’s related to the mysql backend, which defaults to utf-8 and customers having code encoded in latin1 (iso8859-1 or iso8859-15), that is: they’ve encoded their stuff in mysql in latin1. It’s an easy fix, you simply have to specify your mysql encoding when connecting via php, f.example:
$link1 = mysql_connect('localhost','user1','pass1',TRUE);
mysql_selectdb('db1',$link1);
mysql_set_charset('latin1',$link1);
More info at php.net