I think it is somewhat person dependent. I lift just fine on 2 or 3 days of 30-50g carbs per day leading up to a training day. And I am still lifting heavy ass weights (DL, Squat, Bench, etc.). I tend to eat 1 sweet potato after training and usually have a PWO drink that is between 60 - 85g dextrose with 35g whey. But, I haven't been doing that for the past 2 weeks, trying to cut out carbs to see if I can lose some fat more quickly. So far my training hasn't suffered, I am not lethargic or anything and I feel normal.
I would, however, like to have the sweet potato at least because I love those damned things.
People too weak to follow their own dreams will always try to discourage others.