The distinction between less and fewer often causes confusion.
The rule that’s most often given in style guides is to use ‘less’ for quantity and ‘fewer’ for number. Easier said than done!
In ‘Troublesome Words’, Bill Bryson gives a different rule, and one that I think is easier to apply: use ‘less’ with singular nouns and ‘fewer’ with plural nouns (so less alcohol, but fewer drinks; less time, fewer appointments).
A neat illustration of the less vs. fewer problem is a current billboard on display in my neighbourhood. It’s an advertisement from NAB, which says:
This construction seems awkward. I think it’s trying to say that NAB has more satisfied customers than the other major banks do. But the comparisons need thought. It would make sense to say ‘More satisfied customers (than the other major banks)’; it would also make sense to say ‘The most satisfied customers (of the major banks)’. But putting ‘more’ and ‘of’ together makes for very strange reading.
NAB has an ongoing advertising slogan: ‘More give. Less take.’ That works just fine. But it doesn’t work to blindly apply the ‘more … less’ statement to other concepts.