Fair enough. I don't know much about Peripheral Blood Stem Cells in particular, but I am under the impression that stem cells in general are not serving much of a purpose besides waiting around to become differentiated into other cell types.
But I wouldn't be too worried about giving up any of your cells, besides brain/nerve cells.
Almost all our cells have the same genetic information (Red Blood Cells are one exception), so it is theoretically possible to turn one type into just about any other. Shinya Yamanaka's team made a huge step in that direction experimentally about 5 years ago: http://en.wikipedia.org/wiki/Induced_Pluripotent_Stem_Cell
I'm not saying that this is a viable option if you run out of PBSCs (just as it is clearly not yet an option for you to donate skin cells to help Amit), so one thing you may want to find out is if your PBSCs are limited in supply--I don't know (and I am also not in the right demographic for this donation).
I have done the Peripheral extraction thing. You have a needle in each arm, and apart from that slight discomfort you can just sit/lie back and watch TV for a few hours. As tripa says, you get a few days of injections beforehand to stimulate the production - these are subcutaneous, like an insulin shot.
A PBSC-based donation is preceded by a few day's worth of treatment to activate the bones' BSC reproduction, so that they're numerous enough to outgrow the bones and actually become "peripheral". So they're really taking away cells that you usually don't have with you.