If you have multiple offices where each office has its own set of drive letters (mapped drives) you have to type in the full UNC path in order for the relative pathing to work.
For example we have an N drive at each office. The N drive that I work off of is a mapped drive who's location is really \\ONT-E2\projects\ If i load a linked file by browsing to it the path will show up as N:\... Then I try to open that file from another office (with a different drive mapped to N) and Revit wont find the link despite it saying that the link is relative pathed. If I want to be able to open the Revit file from anywhere without mapping to their set of drives first I paste the full path into the open dialogue. Then it will show a path of ..\.....
I have dealt with this before but it really became an issue when trying to specify the loaded worksets of a link in 2010. Aparently 2010 requires an actual .rvt file to be selected before the drop down arrow next to the open button works. Otherwise you can click the drop down button and nothing happens. In this case you have to browse to the file, change the open all to open specify and then paste in the full path.
This is the only way I have found to get a real relative path as well as be able to specify the worksets that I want opened/ closed on a UNC/ mapped drive.
Possibly someone else has dealt with this and has a better solution but this conveluded approach is what I came up with.
Nick