I always send a text- it's nice to appreciate people's company even if you have just enjoyed drinks at a pub and their effort, if they have invited you for a meal.
My circle all do the same. I have several circles- school friends, uni friends, work colleagues, the WAGs, family who we socialise with. I think it must be the done thing in response to your question!
If it has been a wedding or a special occasion like a milestone birthday, I often send a card to say how much we enjoyed the special day. When we got married, several people did this and I put the cards in our memory box.