Borrowing against a 401K is something I would not do unless there was absolutely, positively, no other option. It could possibly happen, but it would be the exception to the rule. Thankfully, I've never had to do so. Tangentially, I remember some years back there were, and probably still are, some companies offering 401K debits. Words fail me on how bad of an idea that is.
This is a very very informative article and it really brings awareness to the dangers. This is an article that is a must read and one that people should keep close to them ever day just so that they can think better before they go out and make bad decisions.
What is the tax penalty and taxes you have to pay if you do not end up paying back your loan? Isn't it like 30% or something ridiculous like that? My 403B is starting to rise at a level that makes me happy...finally!