x1234!! GUMP GUMP GUMP GUMP
Seriously whats so hard about that? GUMP on the downwind, GUMP on base, GUMP on final. People just get WAY to complacent, and in a single piston, VFR, I don't buy the whole "it gets way busy in the cockpit that you sometimes forget". I've never been so busy, even on an IFR flight that I've forgotten to check the gear.
It might not have happened because he was "Too busy" but rather too distracted. Flying by yourself it's easy to -not- get distracted, but you put a second (or third, fourth, etc.) person up there, asking questions, pointing at stuff on the ground, etc. and all of a sudden, you can find yourself distracted right down to the scraping sound.
I recall 3 Eastern Airlines L10-11 pilots who were so distracted by one little green light bulb being burnt out, they flew a perfectly good L10-11 full of passengers into the everglades and everyone died.
And you know the old saw about gear up landings;
"There are those that have, and those that will."
As part of my 1000' callout on final, I always say, "1000 feet, cleared to land, missed approach altitude set, landing check complete, and the gear IS Down." Double redundant? Yes, but I'd rather check it 10 times than miss it once.
It's not about using a checklist, it's about being -distracted- while you are doing the checklist. When I know I've been interupted while doing a CL, I start over from the top.