I want you to know that because of your question, it made a lightbulb go off in my head.
I had some self-employment income (I'm an independent contractor, working part time), and was about to be hit with a sizable income tax bill. Well... since I went on to the vanguard site to get that link to share, I thought ... why don't I open one and put my profit there?
So, it appears that if I max out what I'm able (turbo tax calculated my max allowable contribution for me), then I will be able to reduce my tax bill by about $1500! All while increasing my retirement savings! WIN!
I'm going to open my own individual 401k this week too.
eta:
I think I might be screwed on this for 2013, I may have to plan on this for next year instead.