Just some additions to what I wrote, in light of many useful comments ...
Screamer suggested that you can determine the 'newbieness' of a question simply via it's title. That's valid in many cases, but certainly not all. I would think that the difficulty of the Perl involved would only become apparent with a full reading of the question. Eg. if I titled a question "what is map doing?", maybe it would be a simple case of me not knowing how to use map, or maybe it would be me delving into the perl source code trying to ascertain why an esoteric use of map doesn't behave as expected.
tadman & Ryszard both suggested that ratings may not be entirely accurate for various reasons. Well I would that if ratings are inaccurate then the whole voting system is likely to be inaccurate, for the very same reasons. When you have someone vote on the quality of a post, how is that different from them commenting on its difficulty? The fact that we allow any moderation at all is alreading admitting the possibility of misvoting.
And I would also suggest that the kind of people who go to the effort of moderating and raising themselves through the ranks should be allowed to participate even if they're sometimes off the target. The real dumbos (if you'll excuse my pejorative) aren't likely to be deeply involved in the voting system, and hence won't pollute it.
Since difficulty is a subjective concept anyway, the best way to determine it is by voting! If more perl monks think it's a difficult question, then so be it. Perhaps it could be skewed somewhat by giving higher ranked monks more powerful votes on the difficulty (what about this for the standard voting system as well ?!)
Ryszard also raised the issue of more admin work. This is a valid point - it is more work. But how much more? Selecting a value from a drop down along with either ++/-- is not that bad to me - especially since that activity will probably take far less time than it took to read the node!
I do believe that *some* attempt to categorise questions in this fashion will yield a positive outcome overall. If someone can suggest another rating category aside from 'difficulty', then please do. I'm sure other meta-information about nodes would be just as valid to include as difficulty (or as something to replace difficulty entirely).
ANYWAY! It's all thoughts just thrown up in the air. So chew it up and spit it out if that is your fancy, but hopefully the seed of new ideas might be triggered in people's heads, and that would make any lost XP worthwhile :)
Disclaimer: I have had several glasses of red wine. I cannot held be reshponsible for any shpelling stuff.