In mid-December Autodesk released a new AutoCAD Civil 3D tool. They did it differently.
That was a good thing.
Autodesk released this new development tool on Autodesk Labs and NOT as a traditional Civil 3D Subscription Advantage Pack (SAP). That makes some sense given what it is.
Subassembly Composer for AutoCAD Civil 3D 2011
This is NOT a Civil 3D tool for everyday use.
The SA Composer is a DEVELOPMENT tool.
The SA Composer is also experimental code at this stage. If you are using Autodesk Vault, be careful about installing the SA Composer in it's current incarnation on your production workstation. Odds are you may have a heck of a time getting things put back together. This is experimental code. Treat it that way.
If you have established that you need some of your own custom Subassemblies to solve common corridor cross section issues that are not already in there (supplied in the Civil 3D library), the Subassembly Composer is Way Cool.
If you watch the tutorial videos (available on the page) and if you understand advanced Subassembly operational mechanics, you'll probably be able to construct your own custom Subassembly with it.
There is a basic walk through of the SA Composer's internal mechanics on the Being Civil blog. This post is worth a read BEFORE you download and bang your head on the keyboard. Trust me.
If you want to understand better why Subassemblies act the way they do, Jason Hickey's post is also worth a read.
The Subassembly Composer beats the heck out of the previous methods of getting the Subassembly development task accomplished.
It gives us hope that in the not too distant future More will be possible.