No. If you put new songs inside the iTunes Media folder and rescan for media it will ignore the files that are already part of the library, but if you scan other folders and iTunes is set up to create copies in the media folder then may create duplicates. Immediately after import you can select the Songs list, use Shift > View > Show Exact Duplicates, sort the resulting list on Date Added and delete the recent duplicate imports.
I've also written a script called DeDuper for automating duplicate removal. See this thread for background and take note of the warning to backup your library before deduping..
Message was edited by: turingtest2