The other commenter is wrong: it's totally correct to use "less" with non-count nouns. In such cases, consult a good usage dictionary, like Merriam-Webster's Concise Dictionary of English Usage. This issue is addressed on p.465.

This rule is simple enough and easy enough to follow. It has only one fault—it is not accurate for all usage. If we were to write the rule from the observation of actual usage, it would be the same for fewer: fewer does refer to number among things that are counted. However, it would be different for less: less refers to quantity or amount among things that are measured and to number among things that are counted.