You might recall the recent work by Thomas Rando on selective rejuvenation of mouse tissue: old cells exposed to a younger environment (blood from a genetically identical younger mouse in this case) regain some of their youthful characteristics, such as response to injury. Lou Pagnucco pointed me to an article I'd missed from last month that goes into more detail:
Old cells may regain a youthful phenotype when exposed to a young cell environment ... The results, say the authors, indicate that aged satellite cells have an intrinsic ability to regenerate.
What Rando and colleagues found "argues against the idea that diminishing regenerative potency with age is a reflection of exhaustion of the stem cell population, and this gives great hope for restoring regenerative efficiency in aging individuals, since it is in principle easier to manipulate a systemic signaling system than to restore stem cells to diffuse tissues"
This is very good news when looked at in this light, and certainly merits much more investigation.