[eluser]Myles Wakeham[/eluser]
Well be somewhat careful with blanket statements like this. PHP/CodeIgniter is an awesomely powerful development framework for building all sorts of web based applications. I've built small systems through to huge enterprise PHP solutions with databases containing 400+ tables, and 1500+ stored procedures. All with PHP5 & CI.
But there are weaknesses (mainly in PHP rather than CI). The biggest problem we have encountered is large back-end database processing. We move most of this into stored procedures and run them within the DB when we can. But there are times (particularly with things like large imports) that PHP is just too slow to be workable. In those cases, and keep in mind we deploy solely on Linux, we have written our own binary apps for Linux to do the 'heavy load' work on the server and just call it from PHP. Now that works like a charm.
Also since the PHP application resides on a server, it has a very loosely coupled relationship with the client. Sure, you can use AJAX to communicate in a solid way with the browser. But if you need to talk to local hardware installed on a PC workstation, its going to be a challenge. Not impossible with a bit of local Java or some local application running on the PC using SOAP or something like that to communicate with CI, but still its not something that CI alone is going to be able to solve.
I'm sure there are hundreds of other examples where it just won't be a good fit (ie. embedded device control, real time hardware device handling, etc.). But for the average web application (big or small), it works like a tank. I've been developing in CI since 2006 and still am today. And I've written in a large number of languages before, with most of recent work in C++ & Delphi, so my expectations of a language are pretty high. PHP & CI has lived up to my expectations. Hope it does for you too.
Myles
