I know people register domains based on common typos or spelling mistakes, but is this viable?

How often will someone actually mis type a domain name into the address bar?

It can be valuable, if you have some parking software there like sedo.
If its an $8/year domain, you'll likely make that money back by placing a site or parked software at the domain, so why not

How much can you earn through sedo?
Surely not that much?

Well, I heard that there was this guy who registered a typo of the McDonalds website. He got thousands of hits each month, so I guess it can be valuable.

For a big site like that yes, I imagine it would be popular.
But not just any old typo.. that said, I think google bought up all variations of its name?

I'm sure the guy that parked gogle is making trillions of dollars!

Google isnt parked, google.com has googles search engine on it.
Parked means a domain has no website on it.

So if i can find a mispelling of a famous site i might make money. Im sure most mispellings are already registered so i have missed the boat

Quite often considering how many people are on the net everyday.
Millions of people online, if even 0.1% of those make typos, thats ALOT of people!

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22 sites and counting

yeah true. i didnt think of it that way
so im going to do a test and register some domains like this, park them at sedo and see what sort of traffic i get