Hmm once every few months. If I have an RDO during the week we make sure we have a nice lunch together while DS is at school and DS goes camping with my mum sometimes and has sleepovers there a few times a year.
It doesn't really bother me either way. He's a pest to take out, which is why DP and I go to lunch on my RDOs but we're happy to cook a nice dinner together, watch a movie and share a bit of wine some weekends. We're bits of homebodies anyway so if we had nights together I doubt they would be much different.