<grumpy> :(
2 years run an offline mirror of the site,
ensuring MYSQLI and MYSQL act exactly the same in my situation, duplicating every transaction
Checking and modifying the scripts, there are some dfferences:

backed up the DB, uploaded the altered scripts, went live;
the host crashed
Currently running from the mirror in my basement, till the drive is replaced
(Thank you DynDNS) but damn its slow

It seems, there is always something you can't prepare for
</grumpy> :)