I used to pay my childminder extra for one overnight stay every week - sometimes I'd use it for dating, sometimes just nights out with friends. She was a good friend as well as a childminder, so it was a good rate and I was confident that DS felt comfortable there.
I also did lunch dates when DS started nursery. I live in a city centre location and it was nice to be able to meet guys for a long lunch, often they'd take the afternoon off so we'd see a matinee film or something.
With current DP, he knew it was hard for me to get out, so he made an effort to meet up during school hours. When we got more serious he offered to pay for babysitting so we could get out more. I never wanted him to stay over just because it was convenient though, as I didn't want DS waking up with a strange man in the house. So we've only had overnights when my parents have had DS (on school holidays). But DP is buying a house closer my parents so we'll be able to do a lot more when we're living nearby and they can help out more with babysitting/overnights.