Oh no, I never wake mine up to feed. I did that once and regretted it - he cried and cried and wouldn't go back to sleep. He wakes up to let me know when he's hungry so that's what I go by. Seems to work that way for me, but it's different for everyone. Normally, he eats a 6oz bottle before he goes to bed so that normally holds him awhile.
I agree that they definately go through growth spurts. At around 1 month Zachary was eating constantly and could not seem to get enough..im always worried that Im not feeding him enough but oh does he let us know if he wants more!
For those of you formula feeding..what brand formula are you all using? I'm using Similac Sensitive..