Just brewed this this past weekend. I made a little boo boo, but nothing that should drastically affect the outcome of the brew.
I added 3 gallons (edit: pounds) of the DME at the beginning of the boil, and planned to add the remaining 4 gallons (edit: pounds) nearing the end of the boil. I get to the end of the boil, finish off my hop schedule, and put the kettle in the ice bath, only to realize that I forgot the other 4 lbs of DME. I rushed it back on the burner (by now it had only cooled to 180F) and added the remaining DME. Fearing that I was going to lose a lot of the hop flavor and aroma to the added boil time, I added another ounce of Amarillo (5 oz. total at this point. at flame out. I was saving that ounce for dry-hopping, in case I needed it, but figured this was more important. So I'll probably just end up with a slightly more bitter IPA (which is never really a problem IMO).