If you have to model an existing landscape in Revit, Dynamo can be an excellent tool to automate that process. Not only can you quickly create existing hardscape (that follows Topo), but you can also automatically place and size existing trees using survey data.
In fact, you can use this process to automatically place any element that exists in your AutoCAD survey as a block.
While testing out some Civil 3D CAD links last week, I noticed another strange thing that was happening with some of the links. When the CAD link was reloaded (either manually or by closing and reopening the Revit file), it would actually move within the Revit file. The two images below show where the link started and where it would move. 
It seems to be unrelated to the Civil 3D “splitting” effect, since it also occurs with a standard AutoCAD file. Continue reading
In general, Revit interacts pretty well with AutoCAD .dwg files. Things can start to get a little strange when dealing with large survey and site files, but there are workflows that will keep your Revit file and CAD links manageable (be sure to establish coordinates).
AutoCAD Civil 3D files, however, are an entirely different matter. In the past, I have noticed that sometimes certain survey dwg files would seem to split into two pieces when brought into Revit. Here is an example, where the regular AutoCAD contours and the C3D TINN have split into opposite corners of the current cad link. Even though they are both at the correct z elevation, they are in entirely different x, y locations.
It can be difficult to notice at first, because they will be miles apart, but when you hover over the link, the blue bounding box will extend much larger than it should. The left image is an unsplit link, while the middle and right are two halves of the same link (in plan).
If you are working closely with any discipline that is still using AutoCAD, you will need to export your Revit file to dwg relatively frequently. If you want your dwg export to look like a typical AutoCAD file, the DWG Export Setups will require a bit of tweaking. There are also a few basic settings that when done correctly, will save you time.
For reference, here is what a site plan looks like when exported with the default settings (from the Architectural template).
landarchBIM 