If you plan to have no redundancy, you probably aren't building anything valuable enough to care about losing some data anyways. The extra hours of my life I get back due to productivity from using mongo over something like mysql is worth it x 100. Not a big fan of the single server durability argument.
I agree; I don't get all the fuss about "single server durability." Single servers fail all the time. After many hard lessons learned, I just assume that if it's only on a single server it's as good as gone. Bad RAID controllers, etc.
If you're really worried about durability, you should be replicating anyway--and, ideally, over 3+ nodes at least two datacenters. I've always just assumed MongoDB was designed around that idea.
