Tom is discussing his next venture with his friend Sameer. They have done all the number crunching and are very excited about the opportunity. Everything is finalized and details are worked out. Right, they must be talking about an internet based idea (similar to youtube, orkut, facebook etc).
Next big thing is finding and reserving a perfect domain name for the operation. They started their favorite browser Firefox and jumped on to one of very popular registrar’s website. They started searching their name. They did like some of them but not very catchy. All of sudden someone popped the “perfect name” and got excited to find that it is still available. BINGO! They are happy but still not sure so did not reserve the domain name. They wanted to discuss more and decided to wait for few more days.
After 3 days when they were finally ready to register the domain 
Guess what? It’s gone! They now see a web-spam there which is trying to sell everything from Viagra to “cheap flight tickets”.
This domain was not taken by anyone for years. What happened all of sudden? YOU LEAKED YOUR IDEA.
It is no longer a trade secret that domain-registrars sell their domain search history to “domain junkies” for a decent subscription fee. These junkies grab any good and catchy names immediately and try to re-sell it for bigger bucks. Many simply add them to their pool of domains engaged in pay-per-click based advertisement.
Moral of story is “never wait after finding your perfect domain, reserve it immediately”. If you still want to go with search and wait policy, do not use any registrar site to perform search queries. This can be also done using “whois” command that comes with most of Linux distributions.
A second piece of advice is “make sure you also reserve any similar domains names”. As an example, if you are planning to launch next cool hot deal site http://x1deals.com ; you should also reserve http://x1deal.com ; There can be a big loss due to typo-traffic (traffic generated by typing mistakes) and junkies are hunting for such opportunities.
Hope this helps in saving your next “million dollar idea”
Cheers,
Sudhaker