I agree with juju - I have a big, healthy, usually agreeable baby, and we can loosely follow Gina with no real problems (he can easily cope with going 3 hours between feeds, and has done since 4 weeks old).
However, during a growth spurt I had to abandon for a day or two, and if he has a crap night things go a bit awry. During those times I just try to start the day at 7, finish it at 7 and feed roughly 3 hourly in between.
Have you tried the baby whisperer? Still routine, but far more flexible, and with some sensible suggestions about getting a baby to sleep other than Gina's fantastically optimistic, 'swaddle baby in the dark and close the door' (or words to that effect). Lovely, but what if he screams?
ps - many people on here are v anti Gina, and if you have a tiny/hungry/temperamental baby, I can't imagine it would work in any way. Also, if you are remotely inclined towards co-sleeping/attachment parenting type strategy, I think it's virtually impossible to marry the two ideologies.
Hope you have the confidence to go with the technique that will suit you best!