I have created a "Common Test Framework" project with our test suite that contains constants and common utilities used by the other project within the same test suite. Each project that wishes to utilize one of these scripts simply does an "Add Existing..." to create a reference to the script. However, the icon displayed for such referenced units is no different than that of a unit which actually exsits in that project. It would be nice if the units that are actually references had a slightly different icon than the other units. This can be important when editing units so you clearly know whether the unit is duplicated (meaning you may have to make any changes to all copies of the unit) or whether the file is refernced (meaning that changes to the referenced unit will automatically be picked up by other projects).
Not a big thing, but would help to make things a little more user-friendly.