We were delayed in January because of an evacuation of Newark and our flight got into Newark from BHX at about 7pm by the time we had cleared immigration we had missed the last connection and ended up spending the night in the airport sleeping on the floor, this was not a fun start to our holiday I can assure you.
Coming back our flight from MCO was also delayed and we got into EWR with a 3 minute gap until they were closing the gate, it was a real Home Alone run through the airport - typically we had landed at the exact opposite end of the airport to where our connection was, we literally sprinted and made it with 30 seconds to spare before they closed the plane doors! This was with Continental, and honestly we sprinted through the airport and it was the most stressful 10 minutes of my life - especially knowing that there wasn't another Birmingham connection for 48 hours!! We'd have been stuck there until the Wednesday evening and that was if we got a standby!
Our original outbound connection time was 3 hours, we've found the 90 minutes to be too short, coming back we opt for the shortest connection as there are no bags to check etc so you've only got to get yourself to the gate, where as going out you have to recheck your bags and this can also take some time.
I guess I'm saying that no connection is fool proof, things happen that are out of our (and the airlines) control so it's best to go with what you feel comfortable with - I wouldn't do the 90 minutes again because of the kids, it's a pain trying to co-ordinate bags, kids, car seats, buggies, husbands

etc, but you've got none of these so you will prob be ok with a 90 min slot.
Another thing that my FIL (who works on the planes) always says is if you think you are going to be cutting it fine for your connection then call a hostess and tell them and they can usually arrange for you to get off first or have a buggy waiting to take you through the gates.
HTH
Gems