At least for now, a bitcoin ebay-like site should have auctions listed in USD (or some other mostly stable fiat currency), then grab the current MtGox trading price as soon as the auction ends and have that be the actual dollar amount the buyer owes.
This is quite right!
I think there's a good opportunity for a eBay competitor but it needs to have the right features in order gain momentum.
1. Listings in USD as explained above
2. No auctions to begin with - just Buy It Now Prices (more like eBay Stores)
3. Closely tied to a reputation system (Maybe the OTC rating system)
4. Immediate option to clear to bank account for merchants (Using AutoMtGox or similar)
5. No (or very, very minimal to discourage spam) listing fees (maybe none to start with)
I think this kind of site is an important strategic resource for the BTC community - we all have an interest in something like this becoming successful. For two reasons -
1. The Ebay-Paypal company has close to a monopoly and will never accept payments in BTC because it is an existential threat to Paypal.
2. Selling some old books, cds, dvds or junk in your garage is a great way for new users to get some BTC and start participating. It can also be largely anonymous for them which might be important depending on how they want to spend their BTC.
The main problem to overcome is the chicken-egg problem. You'll see most of the existing sites don't have many listings because they don't have many customers, and don't have many customers because they don't have many listings.
I have some good ideas for overcoming the chicken-egg problem, and I'm interested in talking to interested parties and partners with a view to launching such a competitor. I'm a developer with time and capital, ideal partners therefore are people who understand the potential of BTC
1. Existing eBay merchants with large inventories in existing databases
2. Existing auction site owners (especially BTC the accepting ones above)
3. Persons experienced in SEO / Web Marketing
4. People with a strategic interest in Bitcoin (large holders, miners, business owners)
However I'll talk to anyone who thinks they have something to bring to the party.