Must say I am very impressed on how fast Google Chrome on Ubuntu is. It takes no time to load. It was pain to browse gmail on firefox with firebug enabled and now Gmail is just flying. Very good job. Thank you google team 
These are some interesting links from Google. Little techniques that every PHP developer should make as habits. I think some of them are really effective.
Check those links:
PHP optimization advice from Google
Response to Google’s optimization advices
Another response to Google’s optimization advices
More on PHP performance