There are many reasons to like the Randy Johnson signing if your a Giants fan.
First of all, Johnson is still a very effective pitcher, even at age 45. Last season, Johnson won 11 games with an impressive 3.91 ERA in 184 innings. The Randy Johnson of 2009 will never be confused for the intimidating strikeout machine of the mid nineties, but Johnson still struck out 173 hitters last season. Perhaps the best sign is that Johnson started 30 games last season and did not miss significant time because of injury.
He should be a very effective third or fourth starter for the Giants behind Tim Lincecum, Matt Cain, and maybe Jonathan Sanchez. If the Giants can get anything at all from Barry Zito, then this rotation could be one of the best in baseball. Furthermore, this rotation has great potential to win many games because have a pretty good bullpen on paper with Brian Wilson, Jeremy Affeldt, and Bobby Howry.
Another important factor in this signing is that Johnson is only five wins away from 300. Even though Johnson has never pitched for the Giants before, I'm sure that Giants fans would love to see someone in their uniform achieve one of the highest goals in pitching. Right off the bat, every game Johnson pitches in San Francisco should be a sell out, which is great for the Giants franchise and fan base.
The Giants have done a great job building up pitching depth for 2009, but I'm not sure if they will be legitimate competitors out West. The Giants offense on paper still stinks unless Travis Ishikawa and Pablo Sandoval are the real deal. This team really struggled to score runs last season and they are still in dire need of an impact bat or two.