A friend at work has been telling me since my first month on the job that she should have me over some time. I've always responded favourably, saying, 'That would be great.' Five years later, she still hasn't pulled the trigger. I don't even want to go to her place any more, but it's getting ridiculous. At what point can I press the issue?
You should have started pressing the issue about four-and-a-half years ago.
There's nothing wrong with a shouldvitation: It's a handy way of gauging interest and screening out vegans. But once is plenty; after you've made clear that, yes, you're interested, it's time for the asker to move things along. Next time it happens, say, "How about this Saturday at 7 p.m.? Can't wait!" She'll either take you up on it or never speak to you again.