What happens in LFR varies a /lot/ by battlegroup, time of day, and time of week.
Last week, I ported in to a group in progress (i.e. had already wiped many times) at Will of the Emperor. We then proceeded to wipe nine more times, swapping people in and out amidst massive recriminations, until we finally got some DPS other than myself who could (a) do more than 30k - not a typo - dps and (b) not fixate on the bosses. I hung around as long as I did because it was like watching a trainwreck and because it was the only boss I needed and I knew that regression to the mean would get us over the hump as the baddies left one by one.
Same week, a guildie was grouped with a premade of heroic-geared raiders (presumably dragging an alt through for gear) who could have basically 6-manned the place.
I suspect the chances are better on servers/groups where there is a strong raiding culture. Your mileage will definitely vary.