On the ActsAsFlinn blog, a new article's been posted talking about ActiveRecord and some of the problems with implementing it in PHP.
I'm starting a new job soon and I'll be working primarily with PHP. Since I've been a rubyist for the last 2 years I'm looking at PHP from a Rails development perspective. Before working exclusively with Ruby I hung onto to PHP (because of the project I was working on) by porting Rails bits to PHP. I eventually gave up on porting Rails to PHP after my project's funding was cut.
His experience found that there were a few things that caused the problem in the transition between Ruby and PHP like "in Ruby everything is an object" and some Reflection differences between the two languages. He has a little sample object he's created the code for, but it still doesn't work quite right.
In the end, he points out that the Row Data Gateway is a much easier method to get working in PHP (complete with sample code).