I have a customer who needs a new website and I proposed a Dot Net Nuke soluiton to them.  The customer seems to have a preferance for a PHP solution.  Does anyone know of a white paper which contrasts the pro's and con's of DNN vs PHP? 

As someone who came from a PHP CMS to the DNN CMS (which I think is what yuo were really asking) let me go though some highlights of both from my view point.

PHP; MANY CMS's based on PHP. I used 2 types in my years running a PHP site, MyPHPNuke (a fork of PHPNuke now however the project is more or less dead) and Xoops. The great thing about the PHP CMS's is 98% of all the skins and modules are free. So its a MUCH more economical package to use if that is a concern. And many of the modules and skins are high quality, feature filled. So it is not hard to find a solid module or skin to fill a needed task. On the flip side PHP security issues arose what seemed like bi-monthly thus it is a platform that you -have- to stay on top of from a IT security standpoint. Both from the CMS s/w, modules and the PHP engine itself. I used to use Blackice as a server firewall, network logging tool and it seemed no sooner was a PHP exploit in the wild there were scans and attempted hacks less then 24hrs later in the logs.

The other down side is MyPHPNuke, Xoops, all the module makers and most other PHP based CMS's were the classic linux mindset open source. Which translates, IMO, to a VERY slow, prodding, sporadic dev cycle. At times to many generals and not enough privates. Some years Xoops would have 6 versions others half that (not including critical security patches). Also the ego infighting of the PHP CMS's devs and module creators are legendary. Expect to see forks happen over night, devs jump to another project, the project change focus over night which you find out breaks some of your modules that are no longer being developed/supported and so on. If stability and consistency are very important to you I'd warn you against a PHP CMS.

DNN; as a whole the community and devs have a decent record at releases and consistency. While there may be politics and drama behind the scene they keep it there, behind the scenes and out of the open. I can appreciate and respect that. DNN has far fewer security issues which is also a plus. The down side is except for the core modules your are paying for everything else. It can be expensive, and competition isn't as great as the PHP world. In DNN theres, generally one solid and commanding 3rd party forum, gallery, AD integrator and so on. I think more choice would be a good thing for the community but it is what it is.

Hope that helps.

Two portals that highlight my points about PHP CMS's. One was a fork of the other and the ongoing drama and iffy dev cycles for both make it a challenge for some. However I did not mention those simply because I did not use them, tried them once in test install, wasn't my cup of tea. I can't go into specifics for a product I never used beyond a few hrs. *shrugs* However my overall comments about PHP CMS's are accurate and thats what I was going for, broad brush strokes rather then specific packages in detail. Simply to give him a general picture so he can make a decision not on a specific PHP package but on what platform would suit him better.