Yeah- quick advise - don't do it
hehe
We have a number of servers runing on the PHP 5.3 platform but users are hesitant to move to it because so many other programs are not compatible with the version due to the changes in code. Zend is a big holding back reason for many people. Between that and users having to patch currently "working" software in order to work on the PHP 5.3, people just don't want to make the investment or the move.
That said, we have a few dozen people using PHP 5.3 without issues. Even X-Cart itself, when patched, works on the PHP 5.3 wihtout much of a problem from what we've heard from our clients.
The communication for the general public hasn't been that great with regards to PA-DSS. I actually just talked to a guy yesterday who had no clue what PCI Compliance was, he just wanted his oscommerce store to work (a version from 2003). So it's not just here at X-Cart that people are experiencing frustration, it's the entire industry. People expect the PA-DSS to go the same way as PCI Compliance and not be enforced.
But with regards to PHP 5.3, as long as you disable the depreciation notices, install the patches needed for X-Cart, and then don't need Zend and the software you are using IS compatible on the PHP 5.3 version then there's no issue.
We're also doing some testing currently with PHP 5.3 and LightSpeed. We're still seeing PHP 5.2 ordered daily with web hosting, many people not making the switch yet.