Hi Herman.
If you go to the menu 'Tools' > 'Experimental' , you will find an option to search for duplicates. I believe this is done by name, and will order by folder.
I file by date and event, so have a folder per month (named as YYMM - eg 1008 is August 2010), and any special events or locations I want to seperate out within the month, I create a subfolder under that month (eg 1012/Christmas).
Works quite well for me.
The other thing that you can do to group photos is add tags to a photo. Then you can search for tags using the search function of the 'filters' at the top of the screen (just type in the tag/s you have used as the search key!).
Hope this is helpful.