This add-on allows to limit the number of characters / words in posts / threads.

Features:
Options
Enable minimum characters
Minimum Characters Length
Enable minimum words
Minimum Words Length
UserGroup permissions
Can bypass minimum characters length
Can bypass minimum words length
New features in 2.0.1 :
Options
Enable minimum title characters
Minimum Title Characters Length
Enable maximum title characters
Maximum Title Characters Length
Disallow posts that have only smilies?
Disallow posts that have only bbcode?
UserGroup Permissions
Can bypass minimum title characters length
Can bypass maximum title characters length
New features in 2.0.3 Beta 2 :
Excluded forum
Allow posts that have only IMG BBCode?
Allow posts that have only Media BBCode?
Disallow posts that have only quote?
New features in 2.0.4 Beta 1 :
Added new options
Enable maximum smiles allowed in create thread
Maximum smiles allowed in create thread
Enable maximum smiles allowed in post reply
Maximum smiles allowed in post reply
Enable disallowed words
Disallowed words
Added new permissions
Can bypass maximum smilies
Can bypass disallowed words