usually after a week there should be some signs of carbonation, but i wouldnt worry too much, if after 2 weeks and you still dont have carbonation then i might worry...it all depends though; is it a lager? an ale? a really strong ale or lager? did you use corn sugar or extract? what temp. are the beers at? did you leave head space in the bottles, or fill them up to the cap?
most normal gravity ales should fully carbonate after at least 2 weeks if you used corn sugar...dry extract can take up to a full month (or longer) but either way after the first week there should be some signs of carbonation, i.e. when you pop the top off of the bottle did you here the unmistakable 'psst' of ecaping co2?
you should get this even if the beer tastes flat, after a week there should be some co2 in there that hasnt been absorbed into the beer...