The only time I came close to being IDB'ed was on Air Canada MCO-Toronto, handled by UA agents. The criteria they were using was:
1) pax without seat assignments (7 of us). We had to wait until the end of the boarding process. They did ask very halfheartedly for volunteers, but didn't have any response.
2) Order of check in.

Status wasn't mentioned, but it didn't appear that any of the 7 had status, at least none of them (us) tried to play the status card.

They ended up with two seats available, and luckily I was one of the first to check in, and got one of them. So they left 5 behind and a couple of them were really steamed, yelling at the agents, threatening, etc.