[stephengoodwin]

Facebook originally operated under "thefacebook.com" and bought "facebook.com" for $200,000 in August 2005.[1]

Looking at Crunchbase, they had raised around $13M at that point, so I'm sure spending $200,000 seemed like a lot at the time.[2]

[1] http://mashable.com/2006/08/25/facebook-profile/

[2] https://www.crunchbase.com/organization/facebook/funding-rou...

[CmonDev]

Well, that's 13M that you don't need to give back personally (unlike some bank loan). And .com is pretty important for a site like that. Fb.com is even better though.