@Squirrelmirrel - I wouldn't particularly care. It would totally depend on the context.
The last time this happened was about 15 years ago with this woman who, I have to say, was a bit strange. She was following me around, but this was when the kids were young and I thought she was quite harmless and a bit lonely and just wanted company for her kids. One day she caught me in the street on a Friday afternoon, saying please come to my DH's birthday get-together tomorrow, it's in this room above a pub. Well I just assumed we could pop in for an hour on our way out of town, say hi, have a drink and leave, because this room gets used by lots of people for buffet / drinks type events (I'd even used it myself for that purpose).
But, when we get there, she had the room set up for dinner for about 20 people. So we felt obliged to sit there for hours, eat a three-course dinner. Bear in mind we have 4 kids and they were all bored and the food wasn't really their thing. We didn't know any of her other friends. And then, as we were leaving, she asked us for about £250. We thought we were just dropping by for a drink!
So that behaviour, to me, is extremely rude because she shouid have at least mentioned it was a formal dinner. She just wanted us to make up numbers, I think.
On the other hand, I have 5 girlfriends from uni and we meet up regularly. We'd been talking about going back for a weekend in our old uni town for ages, but never got round to it with kids etc. But when it was one of their 50th's, we did it. We all paid for our own accommodation and the friend bought dinner on the Saturday night. It was a great weekend.