After importing media into a project. Is there a way of showing in the "Project Media" window what media is already on the timeline? Pinnacle has this feature and I found it very useful.
Yes, sure. There is a "Use Count" column, very useful indeed.
Use Count = 0 - Not used
Use Count = 1,2,3 . . n . means used to that amount
As well as a normal Column "Sort", you can also do a simple Boolean search for "Use Count" being equal to 0,1,2,3 . . n or =<n>= and then SAVE that search as a BIN so you can easily filter out your USED or UNUSED media to a separate BIN. Very useful indeed!