No. Dd has stayed away overnight a few times when we have been out late, but not for ages. I just don't see the point really, she is a fab sleeper and goes to sleep without complaining at 7pm every single night, and we don't hear from her until 8 or 9 am. So we wouldn't actually benefit from her being away, I would just miss her! (I was working until I stopped to have ds, so weekends with her were precious!)
Since ds has come along, my mum has minded him a couple of times and my sis has a few times, just for an hour or two. The first time was when he was only a month old and I hated leaving him, but we had to take dd to hospital and I didn't want to expose ds to 'sickie' germs! After that I started to leave him with my lovely hubby for an hour a week whilst I went to weightwatchers, then a few times a week for me to go to the gym. Thats enough for now.
I do agree that its much better for them to get a chance to bond with grannies, etc, and to get used to others. I will start to leave ds more with my mum eventually as she will be minding him when I return to work (thats not until Sept anyway).
My mum minded Amber when I was at work and they are really close, which is lovely.