Where are lineweight settings controlled? Where are Imported Lineweight settings controlled?
Lineweights are configured for each file. If a team is working on one file(worksharing) and one person changes the line settings, the file has new line settings. These are found under the Settings drop down menu. This is also true of Object Styles.
The lesson here is a common one in Revit, if you change it in one place it changes everywhere. So, if you want a thicker linetype, make a new one.
Imported Lineweights are controlled by a text file stored in C:\Program Files\Revit Architecture 2009\Data\ importlineweights-dwg-default.txt. You can edit it and make new ones. These settings do not move with the rvt file, they are particular to a workstation. Potentially two users could import the same file and get different lineweight results.
A team may want to make one of these text files and distribute across the team as needed.