Good question, i've not tried it on PHP 5 yet.
The main issue is the XSLT stuff which the module uses, the API for these functions appears to have changed between PHP 4 and 5 and i'm not sure if it's backwards compatible. The XSLT transformations are an absolute must for the module, it won't work without them. In theory as long as everything else works, fixing this for PHP 5 should be a fairly small job and it is on my to do list for the final release version.
The main issue is the XSLT stuff which the module uses, the API for these functions appears to have changed between PHP 4 and 5 and i'm not sure if it's backwards compatible. The XSLT transformations are an absolute must for the module, it won't work without them. In theory as long as everything else works, fixing this for PHP 5 should be a fairly small job and it is on my to do list for the final release version.