I used the web interface to place a bid on an item. My bid was twice as high as the winning bid, and the myibidder web interface says "My Status: You are the current high bidder". However, ebay does not show me as the winning bidder! I am pretty sure the website has placed my bids on other items. Did I missunderstand part of the instructions?

Was the problem perhaps that I watched the auction ending in my browser?

Never mind - bid was successful. Just didn't know how to evalute this in the ebay interface. Thanks.

I'm glad you got it figured out so quickly.
The simplest way to check is to enable e-mail communications from eBay (so you will get notified from eBay), or check "My eBay" - "Activity" - "Purchase history" on your eBay account.