If you adjust your line-ups by casually looking at the matchup ratings stars that Yahoo displays under Research > Matchup Ratings... be careful.
I just happened to notice the following...
OK, I know that Murph and Davis are left-handers, and that I always check the Ranger line-up when Murph faces lefties and I often bench him. Knowing Buehrle is a lefty, I do a double-take when I see that they both have 5 stars. Checking further, I see that the matchup comment for Davis says:"Slugging 1.091 in 11 ABs against right-handed pitchers in the lower-tier since last year."
So, I hit my magic 'Show Details' button, and I see...
I'm glad that LaRoche has a batting average of .333 vs Oswalt, but the other matchup data says Roy ain't pitchin' tonight.
This is the first time I've noticed errors, but apparently it's simply because the matchup data is out-of-date: Roy hit the DL, and Cassel was called up to pitch. Buehrle wasn't scheduled to pitch today, but was moved up a day. Just a word to the wise, double-check those ratings.