Correct. I learned that too.
Fingerprint check is done instantly and USCIS gets the result back from FBI the same day you get your biometrics done.
Since vk_lk asked and mogambo's posts seem to be edited out, the number to confirm this fingerprint check from FBI is at the bottom of this page:
http://www.fbi.gov/hq/cjisd/iafis.htm
But again, background (a.k.a name) check is another monster and where most people get stuck. Usually senatorial inquiry or infopass appointments tells you if you're stuck or if you've cleared it