Ryan Theriot made his Cubbies debut back in '05 but only played in nine games. In '06 his MLB career started to look more promising, playing in 53 games. In those 53 games he had 134 plate appearances and put up a .328 avg. and .412 OBP.
In 2007 Theriot made the opening day roster as a utility player. He played in six different positions in '07 but snagged the reins at shortstop full-time from the struggling Cesar Izturis, which later led to Izturis being traded that July.
In 2008 Theriot finished sixth in the National League with a .307 average and ranked fourth in the major leagues with 58 multi-hit games. He led the NL with 154 singles.
Theriot has a career .259 average in the final month of the season, and Lou Piniella has said he'd like to have Theriot take a few more days off to stay fresh, so look for Aaron Miles to be the one giving Theriot a breather. Usually you might see the substitution on days the Cubs lineup would face a lefty (due to Miles' switch-hitting ability), but Theriot is just as good vs. left-handers as he is right, and nearly as good on the road as at home in '08.
vs. Left: .305 vs. Right: .308
Home: .310 Away: .304
Day: .302 Night: .311
Theriot's downfall is his lack of power. Last season, among all SS with at least 500 plate appearances, he finished last (19th) in HR, RBI, and 2B.
As I'd hoped and expected, Theriot is lighting it up in preseason spring training. In eight games, he has 21 plate appearances, 10 hits, and just one strikeout. He leads the Cubbies with a .520 OBP and a .476 AVG.