In this new post Lee Blue has gone through and compared Ruby and PHP in a "year end review" of their current statuses and what each of them have to offer:

Now that I’ve been working with Ruby in much more depth and both PHP and Ruby have matured dramatically over the past five years it is time to reevaluate the comparison. The previous article was primarily centered around the languages themselves and was not a showdown between any particular frameworks. In this review we will touch a bit more on frameworks, but in the context of a high level review of the two different landscapes of PHP vs Ruby for web development. We will not be getting down to feature-by-feature detail.

He talks a bit about the history and purpose of each of the languages and a good bit about the web frameworks that are available for each (hint: the PHP options are quite a bit more). He also talks about web hosting vs web application hosting and then compares the two languages with a "score card".

The bottom line, as always, is pick the solution that is right for you and your development team. My hope is that this article was helpful in shedding some light on the strengths of both PHP and Ruby, spreading the word about what is available to both languages, and helping you decide what is right for your next project.