That is very useful, my only complaint would be lack of extensions but I'm expecting you may add them in the future. As I like to check .co.uk, .tv, .fm and .mobi. All of them are in their own rights pretty popular domains. Maybe what you could do is allow people to select which they wish to search for limiting it to 3 at a time. That means there won't be loads of activity but they still get the choice.
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