Well this is certainly interesting. Adam Schefter has tweeted that former New York Giants running back Tiki Barber has filed the necessary paperwork to come out of retirement. The 49ers do have a need for a running back to backup Frank Gore and supplement Anthony Dixon.
It sounds like the Giants still own his rights from when he retired and would need to decide whether to release him or bring him back. We had some discussion about what retirement means in the Carson Palmer situation so this could answer some of those questions. I'll keep an eye out for more information on whether Barber remains under the power of the Giants.
One thing to keep in mind with Barber is that even though he's 35, he retired after his age-31 season. He was a filthy running back when it came to all purpose yards and he would hold some value in a west coast offense. That's not to say I think the 49ers need to roll out whatever it takes to get him. However, he seems like a guy on whom you'd at least want to kick the tires. Maybe nothing comes of it, but you might as well at least do your due diligence.