Not saying I'm successful in the web area, but one thing I try to do is to have some working code before buying a domain name.
Like business cards, buying a domain name makes it seem like you're doing something, but you're really not. You haven't even started; you're just throwing a small amount of money down the drain and dreaming of some future moneymaker.
I'm sure there are many people who have domain names for 1+ years but haven't worked on the product the whole time. I did that once and then learned my lesson!
If it helps, think of buying (and choosing) the domain name as the reward for making something work :)
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EDIT: "playing house" is the term that Paul Graham uses for people who go through the motions of starting a business without understanding what they're doing.