How often does a pre-approved mortgage loan not happen?

I posted some about this on a previous day, so some of you may have already heard it.

My husband Josh and I are in the process of buying our own home. His uncle is a mortgage lender and pre-approved Josh for a $140,000 loan with 100% financing. We don’t have much money right now (we just got married), so he is either waiving or incorporating the closing costs into our loan. He’s helping us out a whole lot and introduced us to a great realtor that helped us find the perfect house.

It’s brand new, has a great warranty, and was listed at $139,900. We met with the building company last night, made an offer, and it was accepted today. Our closing date is set for 60 days from now, but our lender said he’d get it done in 45. We’ve decided to live with my parents in the meantime to save up as much money as we can.

The sold sign is up and all the initial paperwork is done. I’m under the impression the longest part is the loan approval. We’re gathering up my husband’s tax returns, W-2’s, bank statements, etc. How often do things get far along and then the loan falls through? We’ve got connections I suppose, but I’m so paranoid it’ll all fall through somehow.

Any experience/advice would be awesome. We’ve never owned anything but a car, so we’re both excited and nervous about the next two months.