At last month's meetup we discussed the CCK module and I described a bug that I ran into, it happens when you use PHP code in a CCK content type.
If you include php functions in your CCK content type the page is still processed but the "skin" around it (i.e. your theme) isn't processed. Standard PHP code with no functions is just fine but once you add a function (regardless of function type, size, name, etc.)
Its been confirmed by a few others but no solution yet. I found a workaround and had to move on. I hope to return to this bug in the future but right now I'm on a deadline to get 3 sites up and running so... no time..
here's the bug report in case anyonen of you are curious
http://drupal.org/node/76437