It took some digging to find any mention of PHP5 on Pair's site. In fact I only found indirect reference to it beyond the link mentioned above. What I have discovered is that by default Pair uses PHP4. They only use PHP5 if the .PHP5 extension is used or if the .htaccess file instructs the use of PHP5 (e.g. "application/x-httpd-php5cgi html"). I also discovered that PHP5 is installed as a CGI and not as a standard module the way PHP4 is installed. This alone broke a key Apache function call on a test I ran of a few of my pages (I created copies with the .PHP5 extension of a few pages). Once this issue was resolved, things seemed to run just fine.
I'm not sure, however, that I'm ready to switch my site to PHP5 as I will need to do a lot of testing and I'll need to figure out how to install PHP5 on my WinXP box in a similar configuration that Pair uses so that I can test before uploading. Unless I can pull this off, I won't be able to develop in PHP5.
Personally, I'm more interested in the fact that they upgraded MySQL and what this will enable me to do with my queries. I have many queries that I would have preferred to write in a more efficient manner but wasn't able to because of limitations in MySQL.
In regards to the negativity of upgrading or "catching up with the rest of the world" I really haven't seen any compelling evidence that I will realize any benefits from upgrading my sites. Saying PHP5 is faster is nothing but hyperbole that gets used as the reason to upgrade with every software package I've ever used and rarely does it holds true. If PHP5 is really faster, then by how much and why? If I use the same code on PHP5 vs. PHP4 will it really be faster or will it only be faster if I rewrite the code? Security isn't really an issue because PHP4 is still being supported. New functionality isn't really an issue as PHP4 does all I really need to do.
Sometimes upgrading to the latest and greatest version of a program doesn't really provide any real benefit. How many people here are still using Photoshop 6 or 7; Windows 98 or 2000; Office 2000 or older generations of other software? If software does everything one needs, is being supported with security updates and promised performance benefits are elusive, why should one upgrade? Just to hang out on the bleeding edge?
Preaching to people that they should upgrade because they should upgrade turns people off to the idea of upgrading. Disregarding or belittling valid concerns about upgrading also turns them off. If people are to upgrade then it must be easy and provide compelling and tangible benefits. For me MySQL upgrades promise greater possibilities of tangible benefits than does PHP.