We dont do much at all. I have a few cabinet locks left over from when I had my home daycare, but thats it. We dont have stairs, so that's not an issue. We did install a high lock on the front door, because dd1 likes to open it when she hears someone knock, and at 2 ,doesn't realize the danger in that. We dont use chemicals (we use vinegar/essential oils to clean) in the house, so that's not an issue either. The garage is the only place I would somewhat worry, but the chemicals/dangerous things are up very high, everything within her reach is somewhat safe. I guess I don't think many things are innately dangerous, like my sewing machine (this was mentioned in the other thread) I just show her the needle and how it moves and tell her honestly what could happen, same with the plugs. We have a few random plug covers, but more are exposed than not. She was not all that interested in them, so we never really bothered. We have a smallish house, and it's pretty open, so I can see her from wherever I am. I also am pretty vigilant about making sure I can see and hear her, because she is quick and curious (as any healthy toddler is!)
When it comes to others' houses, I don't expect them to baby-proof or be as mindful to dangers as I am. MIL's house is a disaster for a toddler. Open stairs, a pool (without a safety gate) tons of breakables, ect. I don't let dd run around there unless *I* or dh is with her. MIL just doesn't always have the common sense to stay with her on the patio near the pool. And I'm not a freak about it either, I don't hover. If she is near the pool, I simply tell her to walk slowly because the deck is slippery. I don't even go stand next to her, so long as I am within her sight range, so IF she fell in, I could go get her. I'd rather her fall in while I'm there and experience what it is to fall in a pool than to shelter her from it so much that she has no idea what a pool/body of water is like, you know? FTR, she does know how to swim, but still, I'm not comfortable with her out there by herself.
And as for the other things, I think it's just respectful to monitor your children at someone elses house. I certainly dont expect my MIL or my dad to know all the latest about chemicals, toys, dangers. And since they don't live with dd everyday, they have NO idea what she is capable of doing in half a second! So if we are there, I assign either myself or dh to watch her.