Actually, that's a widespread misconception. See here, for example: http://itre.cis.upenn.edu/~myl/languagelog/archives/003775.h...

That's a linguist's take on it - you can find many more by googling [fewer less languagelog] or similar.

That mainly refers to units of time, amounts, etc. "Less than 5 users", I can maybe accept. "Less users", no.