Not sure about what do you mean accountability in this context.
If you specify a little more about your concrete committment, could be great.
For instance, if you have little previous experience you would take advantage from a mentor, a person who is experienced in startups, who could give you advice and follow up your startup process.
Meetups are good places to start looking at, I had help from a former professor with practical experience. Share your concrete doubts and experiences and so on.
This is a brilliant question! It's like Paul Graham says in "How Not to Die": if you could just fully commit yourself to not giving up, your chances of success would be 90%.
This is ridiculously meta but my startup's approach to this is to use Beeminder to hard-commit to averaging one User-Visible Improvement per day.
Here you can see our progress -- we've made over 500 User-Visible Improvements in the last 500 days:
We define a User-Visible Improvement (UVI) as whatever we are willing to tweet as such to http://twitter.com/beemuvi
Obviously we could stretch the definition of a UVI to make it meaningless but since it's public we have too much pride to do that, even with $1000 at stake.
PS/disclosure: I said this was ridiculously meta. Our startup is in fact Beeminder itself. Still, we really think more startups should use this trick! We wouldn't have survived to this point without it.