Has anyone ever analyzed pitcher fielding ratings and the impact they have on performance? I think pitcher fielding ratings vary more than any other position. Some guys have a range of almost 0, while others could be third basemen. Have you noticed a difference in performance/ERA? Is this something worth considering when choosing between a couple pitchers with similar pitching ratings?

Analyzed?  No.   Noticed?  Yes.    As best I can tell, you might get 5 to 7 +/- plays based on good/bad range.   And you might get the same amount of errors from a poor glove.   I've never paid much attention to arm errors or +/- plays because, well, their pitchers and I assume they can throw the ball properly.  

I think the difference of 14 outs(7 + plays as opposed to 7 - or errors) is worth considering if two pitchers are identical.   But I wouldn't put too much time into it.

FWIW, the final numbers from World Major Leagues (just completed season) jive pretty closely with Mike's estimates.

Top (+) among pitchers is 8 (Daniel Jefferies, who isn't out-of-this-world defensively).
Top (-) among pitchers is a tie for 6 (but Fritz Miles did it in only 80.2 innings out of the pen, so that rate is actually atrocious - but so is his D).
The most errors was 7 (Bubba Randolph).