USCIS just returned my money order for the old $170 I-129F fee. They accepted the petition and sent a NOA1, but for some reason, they went ahead and waived the fee even though I only paid $190 for my I-130. In any case, that is not really the point of this post
They sent me a multi-purpose cover letter for mailings related to K3 related I-129F petitions. It has a bunch of choices that they check depending on why they are writing you. Almost all the items are reasons why an I-129F petition is being returned. As I mentioned, they did not return my petition. They also use it when returning a check or money order, which is why I got one.
I thought this might be useful as an aid in avoiding common pitfalls for those who are preparing their I-129F petitions. It's nothing that isn't covered somewhere on the site, but it may be helpful to see what USCIS apparently views as the most common errors.
I am attaching a scan of the cover letter for anyone interested.
Good luck,
CG