HI Doof,
There is a trick I use to AND some properties like people, It is quite simple.
Just setup a view scheme with two (or three) columns of the same property. For example I have set up a view scheme with columns People / People / Places.
Now when you click on some name in the first people column (say Doof) the second column will get populated with all the people that share some picture with Doof. You should find your girlfriend there. Click on your girlfriend's name in the second People column and BAM you only get the pictures with Doff AND his girlfriend (alot of them !:) )
You can do that with more than two instances of the same property.
Another trick I use: I have created a property called 'Subject' for my pictures just to tell the kind of picture it is. It has values such as : landscape, portrait, sunset, etc. plus I have added the following values: People 1, People 2, People 3, People Groups to help me find the number of people inside a picture. Together with the People property you can use this to narrow you research in a big database. For example if you select "People/Doof and Subject/People 2" I bet you'll find the pictures of yourself with your girlfriend !
Hope this helps, Have a nice day,
Christian