I think it depends on your market. If you're aiming for mass-market consumers (i.e. not the people who are reading this comment ;), then .com is pretty important, since many folks don't even know there are other TLDs out there. This is especially true if there's a competitor with the .com -- because lots of people are going to just type your name directly into Google or the search bar and hit enter, and if you're not #1 for your name, you're in trouble.

If you're building something that's targeting our community (hackers, programmers, etc.), there's a lot more flexibility since we "get it" ... I'll just as easily find you if it's .io, .cc, or something more obscure like domai.nr, etc.

I bought a .se domain for a project of mine. In Google Webmaster tools the geographic target is set to Sweden with no way (that I saw) to change it. I got very limited traffic from natural search.

I recently bought a .com domain for the same project and I am already seeing an increase in natural search.