[eluser]GSV Sleeper Service[/eluser]
There's nothing stopping you using php 5 specific stuff in a codeigniter project.
The only real downside of CI's php 4 compatibility is the awkward loading of libraries/models etc eg
Code:
//php 4/CI way
...
$this->load->library('mylib');
$this->mylib->mymethod(); // this just seems awkward to me, my IDE gets confused at this point.
//php 5
...
$mylib = new mylib();
$mylib->mymethod(); // much better, my IDE provides autocomplete etc
I fully understand why Ellis Labs went down the php 4 compatibility route, there are a LOT of hosting companies out there that are still running php 4