The bad thing about pre-approvals is that they aren't done by the underwriters (at least in my experiences). An underwriter gives final determination and can ultimately deny a loan for any reason they see fit. Not trying to scare you away from moving forward, but just be aware that the whole process can be derailed at any time if the UW finds anything they aren't comfortable with. Just be honest and forthcoming with anything they ask, provide all documentation they request, and everything should go smoothly. Pre-approvals are based upon limited information that you provide to the loan officer. It's not over until you have keys in hand and the loan has been funded. Good luck! 
The loan officers typically know what to look for that would possibly derail a loan app, but again, they aren't the underwriters so they can't assure you that everything will go through. I know how you feel, we're going through it right now as well. It's very stressful and time seems like it drags while waiting for updates. The best advice I can give you (which was given to me on here) is to just sit back and let the loan officer and underwriters do their jobs. Like you, they have a vested interest in you closing so if anything comes up, they will contact you right away. Keep your eyes on the bigger picture
Good advice! I just wished I could let go and let them without pulling my hair out, haha! Thank you though, I love this site...it's so good to know how many others are floating along in the same boat with you!