On two different days, a week apart, I talked to eBay customer service people, and complained about losing auctions because of their capcha. Both people said eBay is using them to stop Snipers, and that if enough Buyers and Sellers contact eBay to complain, they may stop using capcha to stop snipes. I don't know how well informed they were, or if this would work.
I have written every seller, every time I've had an AS bid that didn't go through to let them know I lost their item due to my snipe being stopped by eBay capcha, and how much more than the winning bid my snipe bid was. They were all were very unhappy about it, some were furious.