The Giants have the stuff to make another run at the World Series, but they're again faced with the challenge of their division. Last year they barely edged out the Dodgers for a playoff berth, and struggled all year against the Padres and Dodgers, in particular.
Getting Ichiro would provide a needed burst of energy for the shaky batting order this year. They've had a lot of guys cycling around due to injuries and minor league call-ups, and Ichiro would be a force of consistency around which they build.
Lately, Aaron Rowand has been hitting first for SF, and he's doing pretty well this year with a .286 average, but not a lot of explosiveness. He's never swiped more than 20 bags, and he's only hit over .300 twice in his 10 year career. Speed and ability to get on base are probably the two post important parts of hitting leadoff, and Rowand is lacking.
That's not to say, however, that Rowand wouldn't be useful in other parts of the order. If Ichiro hit first, Rowand could move to second, bumping Tejada elsewhere. It's likely that Rowand could move Ichiro along the basepaths frequently, with sacrifices, extra base hits, and even bunts.
Ichiro would probably enjoy the mix of young and old in San Francisco's batting order, as well as a shot at the World Series. The Giants rotation looks pretty nice again this year and Kung-Fu Panda looks strong too.
Of course, it's equally important to see what the Mariners could get out of the trade. I'm going to focus mainly on prospects for compensation in these trades for Ichiro, because the Mariners are looking for young guys who can fill their weak positions, and teams are unlikely to trade the young guys that have just come up to the majors.
The Mariners are soon going to need replacements at SS, 3B, SP, and possibly OF. The Giants' top pitching prospect right now is Zach Wheeler. He has great K/9 and BB/9 rates at 10.9 and 2.2 in the minors over two partial seasons. He's certainly a lucrative option.
Also in the Giants' farm team is power-hitting third baseman Chris Dominguez. He would fit nicely into the 2013 lineup that seems to be coming together nicely for the M's (again, see here).
If the Mariners get Anthony Rendon in the draft, however, shortstop Ehire Adrianza would be a more viable option.
As for a replacement in RF, the Giants might be willing to give up Cody Ross who would provide a nice power asset for Seattle.