After downloading lots of PDFs that open automatically in Skim, I often want to store them all in Papers for reading later.
Here's a little Applescript that will tell Papers to import all the PDFs currently open in Skim:
tell application "Skim"
set filelist to file of documents
tell application "Papers" to open filelist
end tell
Save it in ~/Library/Scripts/Applications/Skim/ and it should show up in the Scripts menu when Skim is active.