To Play-date or not?

Daniel had his first play-date yesterday. It entailed a school friend’s Mom sending me an SMS earlier in the week and asking if our boys could have a play-date.
Up to now I can’t say I’ve ever had an actual thought process about play-dates and what the right etiquette would be.
Let me elaborate:
The Mom, Dad and child arrived and they checked that he was ok and then said they were going and would see us later. Etienne and I did a bit of a ‘huh?’ and I had about 1 000 conflicting emotions ranging from ‘maybe they don’t like me, but their son drove them nuts to play’ to ‘how brave to leave your son’ to ‘OMG, they must trust us enough to look after their sweet little boy’.
It was the weirdest thing for me, especially because I’ve never contemplated leaving any of the kids with someone else unless we know them REALLY well, there’s a crisis or they get paid to look after them. I’ve just kind of assumed the more the merrier, roll on in and let’s have fun.
It was funny when the Mom came back later as I think she picked up on our surprise and asked me about doing play-dates as she was also a ‘virgin’ (thanks C!) and we both had a nervous little chuckle about it. Hilarious!
But now I’m thinking that’s not such a bad idea and I’m really just completely anal retentive about leaving a child with someone else. (unless under the above-mentioned circumstances). I’ve kind of been stuck at the fact that I couldn’t unleash the sheer force of our brood on an unsuspecting family EVER. But suddenly I have options.
Mmmmm…
When did you send your child on their first ‘solo’ play-date? How did it go? Any tips?