Lynn- In true CrossFit form I work backwards towards the science. I use the ZONE'S eyeball method. I also look at my energy levels and coach people to take this into consideration.
Are you hungry in an hour after eating?
How are your workouts progressing?
What does your scale/bodyfat indicate?
What type of cravings or moods are you experiencing?
I know this intuitive process would drive a purest crazy but I found it more real world.
This link presents the eyeball method. http://www.zoneperfect.com/site/cont...ballMethod.asp
I do believe there is a good lesson in learn portions from weighing and measuring but maybe not for everyone.