Here are the current pitching probables for the Phillies-Reds NLDS. There's good news, bad news, and more good news here. The good news is that because the Phils got to choose the NLDS schedule that begins on Wednesday, they can get through the entire series using only their Big Three starters on normal rest. The bad news is that the Reds will be able to do the same thing with their three best starters. The good news is that the Reds do not appear to have taken advantage of that opportunity.
If you go purely by xFIP, the Reds' starters in 2010 were, from best to worst: Edinson Volquez, Homer Bailey, Travis Wood, Johnny Cueto, and Bronson Arroyo. (If you go by SIERA, Wood and Bailey would be flipped.) Nevertheless, Bailey and Wood are the two starters they have elected to drop from the rotation. Presumably this is because they're the two youngest and least experienced of the five. Arroyo has pitched much better in August and September though (3.90 xFIP) than he did earlier in the season, so this might not be that big of a deal.
Volquez is a bit of an x-factor here (which I define as a guy who's performance is potentially as crucial as it is difficult to predict). In the first half of 2008, when he was only 24, he was looking like the NL's next breakout pitching star - so much so that nobody was criticizing the Reds for having traded Josh Hamilton to get him. But then he developed some arm problems, struggled through a mere nine starts in 2009, underwent Tommy John surgery, and tested positive for PEDs in the offseason. He didn't make his first start of 2010 until July 17 and was even sent down to the minors from August 31 to September 7. But since returning, he's pitched four really good games (31 K, 8 BB, 6 ER, 0 HR in 27.2 IP). If he's back to his early-'08 form, watch out.
Finally, here's a video from earlier this year of Johnny Cueto getting hit in the groin with a ball.