Heather O’Cull from the Microsoft Project Development team has a great blog post explaining how Project deals with the rate to consume a resource on a task through the Assignment Units field.  You’ll see there’s some debate from commenters on whether the change in this functionality is the right move but whether you agree or not, this is a key element of Project’s Calculation engine that it’s important to know about just so you know how it works behind the scenes.  For those who do resource calculations in Microsoft Project, I encourage you to take a look.   You can find the post at the Project Dev Team Blog.