The best situation that I have come across so far is that some hosts are still using PHP4 as default for all of their servers, but also provide the ability to use PHP5 either sitewide or per file/directory (eg, using .htaccess). That's the best compromise until the developers provide updates to their applications.

If I'm not mistaken cPanel has problems with PHP5 (or does it just not work at all?) which is the reason why site5.com haven't moved over to PHP5 just yet.

I'm absolutely loving the biggest additions to PHP5, enhanced XML and OOP, both of which are essential components in my everyday coding. XML in PHP4 was indeed a pain in the butt and OOP... well... wasn't too pretty. But things are now much improved (though not quite perfect yet).

Cheers,
Salathe