I've been buying on ebay since 1999, and it looks like I'm averaging about 8 purchases a year. Almost everything I've bought has been rare items (old computers or old software mainly). Also parts that I've needed for client's systems.
I try to keep away from bidding wars. I only bid once, within the last 60 seconds, and only the maximum that I would honestly be willing to pay. I've seen a lot of people pay more for things than they were worth because they got caught up in bidding. I figure that by posting a bid in the last minute, I'm removing the ability to second guess myself.
Yeah, I've lost out on some items... but in the long run, I've been happy being conservative with my high bids.