Project Management Conundrum: Percent Assignment

We all understand what it means when someone is 100% allocated: their entire working time is assigned to some set of tasks. If they're 50% allocated, they have half of their time assigned. It's all pretty straightforward and we all know what it means… but what about from the Project's perspective?

What does percent assignment mean?

Let's say I have a task estimated to take 10 hours and a pair of people to work on it. If I assign 50% to each, then they should each perform 5 hours of the task and they should be done in a single day. Or did I mean something else? Did the 50% actually mean that each of them should spend 50% of their time on it until the task is complete. In this case, sometime on the second day.

Within dotProject, this question comes up quite often. Since Resource Management (aka “people's time”) is still on the drawing board for v3.0, there hasn't been a definitive answer and we've taken the position of “it means what you want” and then we whistle quietly and sneak away while you're not looking. Obviously this isn't a longterm solution, so I put it to you:

What does percent assignment mean to you?