In case you were interested, I posted his win shares below (and Konerko's, for a point of reference).
1999: 23 WS
Keep in mind that an all star player generally gets 20-30 win shares per year, and an everyday player usually gets 10-20. . .This appears to me that Sean Casey is a pretty good player; not a great player, but a good one. He hit his peak in 1999, but I wouldn't say he is spiraling downward into oblivion, as others have suggested that he is. I tend to think that his decline in 2002 is either, a.) health related; or b.) another data point in his tendency to have Jekyll-and-Hyde in-season splits.