Howdy!
When connecting to peers, and periodically as data is moved around, the number of known blocks should be advertised, then the maximal response between currently connected peers shown as an estimate of the expected block count. This would be especially useful for new users to clearly and quickly identify when they have finished their initial local block cache building.
— Alice.
It already exchanges this information.
version message: version 32100, blocks=133643
Maximum is a silly statistic however, since it just takes one silly node to claim an outrageously high value and cause a lot of confusion.
You can ignore values outside of a few standard deviations of the known values exchanged by other peers, which should eliminate fraudulent outliers. The key to this ticket is to show that shared block count value somewhere in the UI.
Poor man's patch http://pastebin.com/ESurLrrL
This was implemented with the bitcoin-qt merge (including a median filter to make sure one fraudulent node doesn't mess up things), closing the issue