Revit MEP - Should we model the Existing?

These are my favorite types of posts... The posts in which my readers get to comment and add all their input to drive the subject.  So please, comment your little hearts out!

We are starting a very large project at my firm and, of course, using Revit.  All disciplines are in house (MEP and Structural).  As I am on the Architecture side of things I am modeling the existing building as I type this post.  In a meeting last week the topic was introduced about do we or do we not model the Existing MEP...

The project will have many construction phases with the existing MEP systems being used during the first one or two major phases.  Then, depending on what the engineers decide, the existing MEP will be demolished completely or bits and pieces demolished.

I would like to ask you, my readers, who may be experienced with Revit MEP and renovations/additions... Do you model the existing MEP components?  Or maybe just the HVAC portion?

Any and all feedback is welcome... I think this will help my readers as much as it will help me.

What's New in Revit MEP 2011 - 90 Second Video Tutorials

I always love the little glimpses into products from Autodesk.  Thanks to Alan over at Revit Learning curve for putting the list together...

What's New in Revit MEP 2011 ~ 90 Second Video Tutorials

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Here are some more Autodesk produced 90 second videos uploaded to YouTube, on the 10th may 2010. These short videos are really useful. however If only Autodesk could actually watch them before posting as the sound quality in this batch is not good as the last lot and could have been adjusted to make these perfect!.

What's New in Revit MEP 2011 - Valves & Fittings – 0:53
It is now possible to place valves, fittings, and other types of duct or piping accessories while in an elevation or section view. For example, you can switch to an elevation view and place a valve in a vertical pipe. You can also add and modify valves and fittings in the 3D view.

What's New in Revit MEP 2011 - Text & Leader Improvements – 1:01
Users can use text formatting keyboard shortcuts and be able to find and replace words within their notes. The leader enhancements include allowing users to set the proper justification for the leader within the top, middle, or bottom locations of the text note and adjust the distance between the leader end and the text note.

Click here to view a few more nice videos from autodesk....