This step wasn't too bad (filling out the form, enclosing a copy of the home study, filling out some other form about releasing information), but the odd part was figuring out where to send it. USCIS has been undergoing some changes to hopefully make the process so quicker, but the location where forms needed to be submitted was changing, and we had to wait a bit. Anyway, it's over, it's done, it's in the mail.
Next step is that we get a letter from them saying they received the I-600A, then another letter with our appointment for fingerprinting.