Scott explains the process well.
It's worth mentioning that with Revit 2011, there is no longer a 4 CPU core limit on processors when rendering, so if you have a dual quad core machine, you can now create rendered walkthroughs in Revit.
Interior scenes with lots of artificial lighting will still take a long time due to Mental Ray calculating the raytracing.
Exterior scenes should render failrly quickly--you just need a computer with multiple processors and fast clock speed.
That said, it is still better to animate and render in 3dsMax, for high-quality visualizations, with its better camera control,
lighting and material editing, etc.
We use both methods; just depends on the scope, budget, schedule and end result you need.
cheers
Cliff B. Collins
Registered Architect The Lamar Johnson Collaborative Architects-St. Louis, MO