I've been going through my code seeing where the enhanced type checking (i.e., the mode toggled by ALT+CTRL+SHIFT-E) in the Scala plug-in breaks down on my code (all of which compiles, of course).
One thing really jumps out at me: Combinator Parsers! Gobs of red!
The combinator operators, e.g.: ~, ~!, ~>, |, ^^, etc. are all flagged "Cannot resolve symbol <op>" (with the actual operator in place of <op>, of course).
I got this result with both 0.3.1807 and 0.3.1814 under IDEA 9.0.3 #95.390.