Just to comment on this thread, I think some people are trying to read a bit too much into certain things.
The example that MikeT posted shows pretty clearly the relationship between +/- and pitching, and it's not that difficult to quantify.
Adjusting for IP, Mike's pitchers allowed about 61 fewer non-HR hits in S10 than they did in S9. Their +/- was 53 better. Pretty simple. Generally speaking, for every 1 increase in +/-, you save about 1 hit. You can ballpark the value of a hit at about a half of a run. So, every 1 increase in +/- saves you about half a run. Not too complicated.