Hi Tom,
I've done some quick testing on my test server (which is using version PHP version 5.5.3) using version 2.09, and didn't run into any major issues. The only problem I came across was a function depreciated warning that displays at the top of the CMS on all pages. But a lot of servers automatically suppress depreciated warnings, and I can give you the code to hide it if does appear on your server.
I run the latest version of CMS Builder on same test server, and have not come across any issues.
Let me know if you have any questions.
Thanks!
Greg
Greg Thomas
PHP Programmer - interactivetools.com