While I have been at university studying a CS degree I have been picking up web development on the side. As I started in the last couple of years, I have mainly been using Rack/Ruby based frameworks such as Rails and Sinatra but I have also looked at - and occasionally used - Web.py, Django and Lift. I realised that I have never used or seen PHP used for web development. This might seem strange but, as a young twenty something, learning PHP doesn't seem like the most fun/hip route to take.
Given this background (which I am sure is relevant to many people my age). What is the best way to approach learning PHP web development? What are the key differences/similarities? Also, what frameworks are widely used and/or respected?