Projected goals allowed by goalkeepers

Dave Clark of Sounder at Heart sent me an interesting post he wrote last month in which he attempted to project the number of goals allowed by Sounders 'keeper Kasey Keller over the course of a MLS season.  He bases this projection on the goalkeeping statistics from previous seasons (or is it just last season?), allowing for adjustments for league quality and the defensive backline.  I have to admit that I'm confused about the formula that he used; I wasn't able to follow it from his written description. 

Nevertheless, I think the statistic has some promise and makes use of the data available.  I'm curious to find out whether penalties are included in the shot calculation.  There are some goalkeepers who are quite good at saving those (10-15% to make a SWAG), and those shots on goal are very different from any other shot on goal during the match.  The high level of correlation between shot/goal ratio and goals-against-average is very interesting, but it would be nice to see a scatter plot of the SGR against GAA for a variety of goalkeepers to determine whether the relationship is linear, or even approximately linear.

It's a prediction that's worth exploring for a number of 'keepers in MLS, and the season is two matches old so such a forecast would still be useful.  

I saw that Dave has some additional stat analysis of Sounders matches on his site.  I need to check those out later, but for now I wanted to get this post out of the way so that he doesn't think I'm blowing him off!