Stack Overflow calculates entropy of a thread as a signifier of low quality.

As an admin of a largish forum I find these attempts to sort people and their output algorithmically very interesting.

Could low entropy of a string be reasonably substituted by a short length as a symptom of low quality?

What mathematical property of a text could signify high-quality posts?

I think Slashdot has been using gzip to detect spam for a while — anything that's too highly compressible or completely incompressible isn't English text.