Robert_Charlton - 9:21 pm on Sep 21, 2011 (gmt 0)
This has been around for quite a while, first as an Advanced Search feature in 2010, and then as a sidebar feature.
In the March 2011 update thread [webmasterworld.com...] in a March 24, 2011 post, tedster mentioned it as one of the factors he was watching....
Some other on-page areas I'm exploring:
1. Reading level (Google rolled this information into the SERPs after they started work on Panda this past year)
2. Semantic richness, as detailed in the phrase-based indexing patents
3. Spelling and grammar.
There's also this discussion, among others...
Reading Level and Panda
Apr 19, 2011
I think that reading level needs to be appropriate to the kind of query vocabulary you're targeting. I'm sure it also ties in with user demographics.