DS was invited to a big birthday party for 4 boys from school turning 7. They'd hired a venue, and had a cool activity for the boys to do. One mum emailed and said rather than parents buying gifts, they would like cash gifts.
This went against the grain a bit for me, but I put £10 in 4 cards, one for each boy. This was at the end of November, and we've not had one thank you message from any boy (or mum).
I've not thanked them for the party either - I guess it was expensive - asking for cash then not saying thanks is a bad lesson for the boys, no? One parent was telling me their son got over £150 to spend and didn't know what to buy - but still didn't say anything about our contribution.