A LONG time ago Dana Probert suggested a method to grab styles from one file and quickly add them to the current file (V1.0).  Engineered Efficiency created a tool and placed it in their ProPack (V2.0).  You can find the post here http://civil3drocks.blogspot.com/2006/07/super-secret-style-getter.html.

Civil 3D 2011 has two new tools.  Read on…

Now, you won’t find these two tools in the help file, or what’s new, or anywhere unless you know someone who already knows or you completely stumble upon them while cycling through all of the AECC… commands in the command line.

As with all undocumented commands and tools, these are undocumented for a reason.  Your guess is as good as mine as to why they are undocumented.  Maybe more will be added later on, who knows.  These commands do what they’re supposed to do, so it is what it is.

Peter Funk explained them in a Civil 3D discussion group post.
http://discussion.autodesk.com/forums/thread.jspa?threadID=774989&tstart=0

#1 – AECCIMPORTSTYLES
This tool will grab styles from any selected file and transfer them into the current file.

#2 – AECCIMPORTSTYLESANDSETTINGS
This tool will grab styles and settings from any selected file and transfer them into the current file.

Verbatim from Peter’s post:

These commands will prompt (at the command line) for a template (dwg or dwt) file that will be used as the source for the styles/settings. Then all the style/settings from the source drawing will be added to the current drawing. All the styles will be imported.
NOTE: the styles in the source drawing "win" – that is the current drawing is modified to match the template file.
NOTE 2: This is a command line only prompt – there is no file dialog by design. This was done so that the command could be scripted to run on a set of files.

• The routine will ask for a path to the DWT or DWG file to be used as the source.  It’s asking for Path and Filename.  For example, this is what the routine wants;
  C:\My Files\Civil 3D 2011.dwt
• DO NOT assume that because you have spaces, you need to enclose this in quotes; the routine will just end without notification.  If it appears to have done nothing, it’s very likely you spelled something wrong.
• This routine currently appears not to affect anything other than the styles and their direct settings.  Meaning, no settings seem to be imported from the Edit Drawing Settings, or Edit Label Style Defaults, or Object Layers, or Ambient Settings sections.

Enjoy,
Matt Kolberg