New Scientist Magazine reports Typos may earn Google $500m a year: Google may be earning an alleged $500 million a year via companies and individuals who register deceptive website addresses."
If Sweet Expectations, Auckland's custom baker and wholesaler of muffins, was a top ranking site that had millions of hits each month, this could bring the typosquatter thousands of hits from people who had poor keyboard skills induced by low blood sugar from lack of freshly baked treats, and as qualified traffic is relatively easy to convert into money through adverts could make a respectable amount of money.
Actually it doesn't matter much if someone has a site on that name or not. If it's an obvious typo for your site name and you don't cover it, you will lose a percentage of your type-in traffic. Tessa and I have faced this problem last year when the Yellow pages put the singular Sweet Expectation URL against her listing instead of the correct one. We fixed this by immediately registering the singular domain name & fixing the problem at Yellow Pages the next day. I've kept the registration current as its' a cheap price to pay for catching the most obvious typo.
Assuming traffic is worth it to you, you should consider your domain name and the most common typos of your company name and cover them too. The traffic you save will be your own.