PHP6 .. whats new in it?

Unicode

Unicode support at present can be set on a per request basis. This equates to PHP having to store both Unicode and non-Unicode variants of class, method and function names in the symbol tables. In short - it uses up more resources. Their decision is to make the Unicode setting server wide, not request wide. Turning Unicode off where not required can help performance and they quote some string functions as being up to 300% slower and whole applications 25% slower as a result. The decision to move it to the php.ini in my mind does take the control away from the user, and puts it into the hands of the Web Host.

If you compile PHP yourself or are responsible for this on your servers then you may be interested to know that PHP 6 will require the ICU libs (regardless if Unicode is turned on or off). The build system will bail out if the required ICU libs cannot be found. In a nutshell, you'll have another thing to install if you want to compile PHP.