Where are you coming from? Atlanta is usually very easy- only time I had problems was when coming from a country with some outbreak. Usually the hold up is getting bags through and clearing security. You should be fine.
Thanks mundo and Sarni for that information! One time I got off the cruise ship they forced me and my husband (he is a citizen) to go in the non-citizen line....last time they also had us go to the non-citizen line.
The signs at ORD said "US citizen" and so I never thought to go into it!
2.5 hours is just fine.
We came back on Sunday through Atlanta at 7pm from Cancun and it was pretty busy, had to wait in line for a bit, but managed to make our connecting flight which took off at 8:30pm. I was a bit concerned because we didn't get our luggage rechecked until about 7:50pm, but it arrived just fine at our final destination.
Yep, you'll be fine - I remember a few years ago ATL was a huge cluster and I still got through in about an hour. I'm not sure if it was just busy or if they were remodeling or something. In March of this year I got through in 40 minutes.