This is the definitive statement on loading libraries. I'm putting it in the Standards panel of the sidebar. Like the other standards things, it will probably be updated occasionally.
Update: From the Project Libraries, only load the folder for the current project.
Tell me one more time what's in the libraries.
Objects, doors, windows, lamps, skylights, zone stamps, section markers, detail markers, databases, list schemes, properties, textures, background images. Not much, really.
Attributes, work environment schemes, display option combinations, view sets, interactive schedule settings, dimension standards.
Which libraries should be loaded.
More on what libraries are where can be found here. Version numbers in library names (LIB11, e.g.) will change periodically.
From the carrot (2 Libraries): 1 Rill & Decker LIB11.
From 2 Libraries / Master LIB 11 / 2 Project LIB11: only the folder for the project. Don't load the whole 2 Project LIB11 folder. This will cause duplicates; see duplicates below. Create project library folders as they are needed.
From your local disk: For AC11, ArchiCAD Library 11, the entire folder. Its location is Applications/Graphisoft/Archicad 11. (For AC9, ArchiCAD Library 9.pla, located at Applications/Graphisoft/ArchiCAD 9/ArchiCAD Library 9. Load only the pla archive file, not the folder. It probably doesn't make a difference, but this is the recommended technique from Graphisoft.)
Why are our libraries on a server.
So we all have the up-to-date library all the time. I update library parts frequently.
Why is the ArchiCAD Library loaded locally.
Because it loads faster. Since the AC library only changes when GS updates ArchiCAD, we are all up-to-date without using the same exact resource.
Can I copy the carrot libraries to my local disk and load them from there.
I do not support this. Again, I update library parts almost every day. If you are using a local copy, you are out of date. You could copy them every day, but this isn't any faster than loading them directly from the server. We sacrifice a few seconds of loading time for the benefit of having one consistent library for everyone.
But I thought local libraries are faster.
They load faster, a little. Once the libraries are loaded, there is no performance difference. As library parts are placed in a project, their code is cached so that their continuing use is faster. The objects are not read from the server as you work in a project. They are read from this cache.
What about the cache library, sometimes known as the satellite library.
The cache library sounds like the perfect compromise between having server libraries and local libraries. The library is shared, but AC builds a local copy whenever libraries are loaded, keeping the two copies in sync. But I can't recommend it. It's a great feature, but for some reason it's especially vulnerable to bugs. Every once in a while you get an update that breaks it. It's not worth it.
Tell me about the History tab in the Library Manager.
The History tab remembers libraries you have loaded in the past. With a little discipline, it's a great help in getting the right libraries fast. Your History should only show a) carrot libraries, and b) the local AC library pla.
The History never contains actual duplicates. if you see duplicate names, you have the same resource on different paths. All but one of these paths is wrong. You can see the path of each History item by highlighting it. If it starts with anything other than '2 Libraries' or the name of the local machine, delete it. Note: If you've recently upgraded your computer, some History names will point to your old computer. You need to fix this manually and delete the old ones. In fact, if your history list gets long, it's easiest to clear the whole thing and start fresh.
The history is especially helpful if you work on two machines. The History on each machine will give the valid libraries for that machine. So when you open a project at home, you'll get the Library Manager telling you libraries are missing, but the History tab makes it easy to load the right ones. When you bring the project back to your desktop, same deal.
Some object isn't working right.
Tell me. Wait, back up a little. Before you tell me, reload the libraries. Some apparent problems are caused by my fooling around with things, and you just need to get the latest version of something. Tell me even if it's an AC object; I can probably help you work around its issue.
All the objects are missing.
Make sure the carrot is mounted. If it isn't: In the Finder, Connect to Server (Cmd+K, the blue circle '?' button). The server's address ends in 99.
The Library Loading Report says things are missing.
Do not ignore missing objects. These directly affect the project itself. (Exception: Sometimes a zone stamp will be reported missing when it isn't, it was merely in use in the previously open project. Bug.) Tracking down missing parts in very old projects can be a chore, but I know you can handle it. Ask for help.
The Library Loading Report says duplicates.
Generally, do not ignore duplicates. Try to resolve the issue. Ask for help if needed. If you have duplicate objects, you can't be sure that the one that gets used is the right one; it may be that the other one is more current.
You will often get duplicates when opening an old project. If you determine that the duplicates are from the ArchiCAD library, you may be able to let it go. If the duplicates are from the old Smart Parts library, you can definitely let it go; those objects have never changed.
Another problem with tolerating duplicates is that you get used to seeing the report pop up, and you ignore it, and when it says something important you've stopped paying attention.
How do I get the Report back if I close it.
Window -> Palette Display -> Show Library Loading Report.