I'm on the fence about this. I did participate in this, simply because I was already losing the auction and I figured it would be a nice thing to do. But I hadn't really looked through the eyes of the other bidders until now. It is hard to form an opinion on because the basis of the act is purely out of kindness, however I do have a few things that I don't think are right.
First of all, I really don't appreciate people rooting for a specific person. It makes the rest of the bidders feel alienated and it is hurtful. And although it may not be directly said, bidding pins for others is a blatant way of rooting for a specific person to win. And then often other members, again, out of kindness, jump on the bandwagon and add to that one members bid as well, and it sends a clear message to the other bidders that "We want this person to win" ergo, we don't want you to win.
And that is where my second problem is - feeling guilty about bidding against one of these bids. Normally, when people bid for others, there may be some sort of message about how nice they are, how much they deserve it, etc., which is why various members are trying to help them out. (And even if there isn't any of this said, with so many people supporting this person, it gives the obvious impression that they're well liked, and of course that is so because they're a nice member.) I'm sure that's all lovely and true, but now I have to feel guilty about bidding against them, which is really not at all fair. All these people are hoping this person they're supporting and bidding pins for wins, and if I bid against them, I look like the bad guy. I have to go against this person described as so wonderful and so deserving of this pin (which they probably are, but hey, it's more than likely that all of the bidders are just as nice and deserving), and that just feels awkward because everyone is rooting for them and you look like a jerk bidding against them.
Although it's an extremely nice gesture, bidding for others implies you rooting for one specific person, and that hurts the feelings of the rest of the bidders. And now, the other bidders are in an awkward position because it makes them feel like they're obligated to let that other person win or possibly even support them. It's like peer pressure - all these people are supporting this one person, do I now have to support them/let them win so I don't look like a jerk, or bid against them and upset all these people and ruin their nice gesture? It's not fair that anyone should feel hurt because a crowd is rooting for a specific person through bidding for them, and it's not fair that they are than felt pressured to go with the crowd to support that person, or risk looking like a jerk.
I know that bids for others are out of kindness, but they do hurt the other bidder's feelings, and if you really want to support this specific member, I'd suggest doing it privately:
1) PM the person you wish to support and list the pin(s) you'd like to add to their bid
2) Have them reply with an agreement/disagreement
3) The original bidder PMs the auctioneer, letting them know that should they win the auction, the addition pin(s) would be mailed from a different member
4) The original bidder adds the pins to their bid in the auction thread, so the auctioneer can have the entire bid in one place, but do not indicate which pins are in your possession and which pins, upon winning would be sent by another member. (The auctioneer already knows about this, and not mentioning it avoids hurting other bidder's feelings). Simply list them all as your own, single bid.
5) Should this person win the auction, they send the pins they have in their possession to the auctioneer and the person that offered to bid the additional pins sends those pins to the auctioneer, and the auctioneer sends the auction pin to the original bidder.
This private way would eliminate any implication of people rooting for a specific person and thus hoping another member does not win, and would then also avoid the "peer pressure/going against the crowd" aspect as the other bidders have no idea, and they really don't need to know anyway. If you want to add to a person's bid, it should be between you, the person you're supporting, and the auctioneer.