Starbuckone:
Where 'discrete' quantities are involved (e.g things which can only be counted as 1, 2, 3, etc) the correct word is 'fewer'.
Where 'continuous' quantities are involved (where, for instance you could have 2.368 of them or the square root of 43 of them) the correct word is 'less'.
You can't, for example, have 2.368 people. You can only have whole numbers of them. So we refer to 'fewer people', not 'less people' and, as Factor 30 states, 'fewer items', not 'less items'.
However the quantity wine in your glass is not measured solely in whole units. So you have 'less wine', not 'fewer wine'.