Yesterday's DL 1075 MEM-LAX departed ontime yesterday. I knew something was amiss because we leveled out right after takeoff. The Captain informed us over the intercom that we had to return to MEM due to cargo being loaded incorrectly. Was a 738, no AVOD.

So, we returned to MEM where the station manager, a lady wearing a safety vest, boarded the flight and apologized for the delay and told us that we could leave the a/c but they would appreciate it if we would not as we would be on our way soon. After about an hour more, we did indeed get underway and were about an hour and a half late getting into LAX.

I am very appreciative that DL kept me safe and got me to my destination with a bearable delay. I am not looking for miles and/or sympathy.

My questions:

1) What kind of cargo loading error would result in an a/c returning?
2) How is it that such an error was discovered, and then only discovered after takeoff?
3) As it is a fairly long domestic flight, was there any additional risk in landing with the amount of fuel gauged to get us to LAX when we only flew for 10 minutes or so, or are such risks generally only for much longer TPACs and TATLs with larger a/c?

Again, I'm just mostly curious if any FTers have a clue as to how/why this happened as it was a first for me.