One reason I prefer FeedDemon over Google reader is the pace at which I can navigate between the feeds and perform operations on the feeds/news items. Google Reader is fast but its still a long way from matching the speed of a desktop app. Its the exact difference you find even in eBay Desktop compared to its web peer.
I don’t do much of shopping on eBay but definitely use it to track/watch the price of some of the gadgets which are on my wish list ! If you are a serious eBay buyer or seller, eBay Desktop is worth a try !