Why would the problem be solved if there were 100 other BTC trading sites created?
Everyone would still stay on the best site. There are thousands of search engines in the world, everyone still uses Google.
To prevent this from happening there should be like a user cap on every BTC trading website. But that wouldn't work because everyone would cry that they can't register on the best BTC website.
I only use google for image searches or when I can't find what I want with duckduckgo.
The reason I want multiple exchanges is that competition is good for the consumer.
When exchanges have to compets for us, they are more likely to innovate and provide fair pricing.
There are several concerns I personally have with Mt. Gox
A) They are not located in the United States, the country I reside in. This makes legal disputes (should they occur) more difficult to settle.
B) They lied to FinCEN. Now maybe that wasn't intentional, may have just been a mis-understanding, but they need people who understand the forms and how to answer them.
C) There are way too many reports of withdrawals taking way longer than they should. That worries me that there is funny business going on and I don't want my money passing through hands where there is funny business going on.