How many versions of Revit does it take to work as a consultant? Well, it takes as many versions as your clients choose to use. As a consultant, you work for a variety of clients, that may be on any given version of any given software.
In the DWG world, we have simply become experts at converting formats and versions up and down as needed. If I'm on 2010 but you use R14, no biggie, I can even convert MicroStation files as needed.
In the RVT world, I have projects in Revit 2009 that will not be migrated for what ever reason by my clients. Two of these projects will be in my office for the next 3-4 years. That means I will keep Revit MEP 2009 on my users PCs until 2012. I will be using Revit MEP 2013 by that time. Does this mean I may have 5 versions of Revit running to satisfy the needs of all my clients? Unless something changes... Yes. (Will my PC be able to handle that?)
Where before, my users opened the current version of AutoCAD (MEP) and worked in it all day converting when needed, now they will jump from one version of Revit to another depending on the job they are working on.
I understand the benefits behind restricting compatibility with Revit products, at the same time I really wish I could dumb something down when I need to.
There is a really good chance that I have missed something simple here, so if you know something I don't, please comment. In fact no matter where you stand, I would like to hear about it.