I like PHP Nuke and all it can do, the skins look great, however when ever someone does switch over to a PHP Nuke Site, it is hard to get any credibility.
The site is nice, however for respect in a web-designing community [if you care] i'd suggest designing something yourself, its much more satisfying to complete something great that you made, than to install a web-software. Even if its total crap, you can learn more from designing something yourself.