The day before this episode aired (so right after I was freaking out about how could Sayid "kill" Ben in the past if he exists in the future) reader Stefan wrote:
First rule is: what happened, happened. Based on that notion, Sayid did shoot Ben, in the spine. Ben does not die from this, but is probably saved (reluctantly) by Jack. Something goes wrong with the operation, or just the damage that is left creates scar tissue that becomes a tumor that Jack then needs to fix 30 years from then (i.e. now). I looked at a screen shot of the X-ray from season 3 and it looks like a circle or hole in one of the vertebra. I'm not a doctor so I don't know for sure.
Don't blame Stefan for the Jack speculation, as I said, he wrote before this episode aired. But it's pretty nice midrash, all the same. Unless or until I see this contradicted on screen, I'm going to keep this theory, pet it, and name it George. Thanks, Stefan.
Cindy McLennan also covers How I Met Your Mother and Cupid (it's gonna die, brotha) for TWoP. If you have a Lost theory you want to share, or need to call her out for picking on the name Clementine this week, you can write to her at CindyMcLennan[at]gmail.com. All you Candidas and Cynthias, your concerns have been heard and are being addres -- oh just buck up and get to the back of the line.