Wish in one hand...
I received Revit MEP 2009 a couple of weeks ago, and have started digging into it. I had high hopes for 2009 myself.
The valve library is larger than it was in the 2008 version, but falls far short of meeting a real-world piping designer's needs. All the valves are generic.
Now you can draw pipe in an elevation view, but you have to make sure that the pipe you want to start from is closest to you in the view. That means that you have to cut a section to isolate the pipe you want to start from and draw in that section.
However, you still cannot effectively draw piping in a 3D view. Revit wants to draw in the XY plane. You can draw piping between pipe connectors in the 3D view, and, if you have everything lined up horizontally, Revit makes a reasonable looking connection. If everything is not lined up, you'll get 17 degree elbows and who knows what else.
What we need, guys, is the ability to draw in the three principal directions in a 3D view. Plumbing designers have to submit riser diagrams, and they are typically isometric views. You can draw the horizontal sanitary waste and vent piping in plan view, and now you can draw the risers and revents in elevation views, but there are still occasions when you want to draw in the isometric view. The cute little view cube would be the perfect tool for setting the active work plane, but, alas, it just changes the view direction. However, it is a great tool for setting the view direction.
Maybe in the 2010 version...