The fact that the addition of Aaron Rowand probably makes the Giants a better club in 2008 should not be seen as an endorsement of the signing. We're talking about a lineup where the fourth-best hitter is the "VACANT" sign hanging on third base.
Rowand is a dead-fastball hitter with a complicated, high-effort swing that produces a lot of sound and fury, but a lot of swings and misses as well. His power is part real and part the effect of the hitters' parks where he's spent his entire career (56 homers at home versus 37 on the road). He's not enough of a contact hitter to predict high averages, and his batting average has fluctuated accordingly throughout his career. He is not patient, going after the first fastball he sees (or thinks he sees), never drawing more than 44 unintentional walks in a season. He's now moving to a bigger ballpark that's about as unfriendly to home runs as Philadelphia's park is friendly to them, and he's not going to make up for the loss of that power with good OBPs.
Jerry Crasnick just named the Giants' lineup (without Rowand) the worst in the majors as currently constructed, and lack of on-base skills is a major reason. The Giants' offense revolved around Barry Bonds, who certainly won't be playing in San Francisco in 2008, leaving the Giants with a sort of baseball anemia. Bonds drew 132 walks in 2007; the rest of the Giants drew 400, with no one over 53. In fact, the Giants put fewer men on base in 2007 than any other NL club but Arizona, and that's including Bonds and his .480 OBP. If you don't put men on base, you don't score. Signing Rowand doesn't help the Giants on this score.
Rowand might lead the Giants in home runs in 2008, but that's again a reflection of his new teammates. No returning Giant hit more than 19 homers in 2007; the top two Giants in that category, Bonds and Pedro Feliz, have both left for free agency.
To the extent that Rowand takes at-bats away from Rajai Davis and Dave Roberts, he'll certainly help, but he doesn't move this club forward significantly. And if Rowand, who has spent his entire career in great home-run parks, sees a major power outage with the move to power-killing AT&T Park (a little tougher on left-handed hitters than right-handed, though), then the Giants aren't really helping themselves in either the power or patience department.
On defense, Rowand's prowess is greatly overrated because of his tendency to make "tough" catches, and his fondness for running into the center-field wall. His range and arm are both average, and he's moving to a big center field that might expose his lack of total range. Rowand is a small upgrade over Roberts, but probably isn't any better than the erratic Randy Winn in center, and his addition leaves Roberts out of a job, since he doesn't hit enough to play an outfield corner. There's also a chance that Fred Lewis will end up on the trading block as well, assuming that the Giants don't want to dump Roberts' contract and insist on playing him and Winn in the corners.
The Giants just gave a very good fourth outfielder who's stretched as an everyday player in most years five years and $60 million. It's reminiscent of the Angels' signing of Gary Matthews Jr. last winter -- a deal they regretted enough to replace him this winter. But the Giants' in-house alternatives were bad enough that the Rowand deal does make them a win or two better per year in the short term. They're not going to get their money's worth, nor was it worth giving up a second-round pick to sign him, and since the Giants are not likely to contend for at least the first three years of Rowand's deal, it's hard to see why they'd move to make such a large and lengthy commitment.