Today on UA648 ORD-LGA, we had to deplane and board a substitute when they couldn't get one of the doors to close. We ended up departing about three and a half hours late, compounded by delays transferring bags and their failure to remember to transfer the catering. (We ended up going without catering, which meant the snacks in F were limited to bags of pretzels, but by that point we were all happy just to take off.) The flight attendants handed out SkyKits in F, and I had an apology email waiting when we landed. Offered 9K miles, $200 domestic cert, or 10% economy coupon; I took the $200. I wasn't pleased with the bumbling on the ground, but the proactive apology was unexpected and quick.