Right now, we don't have any small Legos in the house - just Duplo. But I can remember stepping on them as a kid. We had an old braided rug in the livingroom and no matter how hard we tried, we ended up forgetting at least one of the tiny, one-bump pieces (usually blue or black cause it blended so well) and inevitably it was mom who "found" it the hard way and boy did we hear about it!
As for first hand, recent experiences, the small wooden triangle shaped blocks are pretty bad too. Especially when on a hard floor. Shaped just right that there's no way to kinda step on it, and it's always right in the middle of your arch.
I've found the easiest way to avoid stepping on things is to avoid going into the playroom
. I go in maybe once or twice a week to straighten things up and just start at the door and work my way in.