Is there a way to get rid of the 4 tabs? How about split the description-field into 2 fields: type and description. The sorting by type would have the same functionality as those tabs. What is more interessting IMHO is a textfield for filtering the data below.
Yes getting rid of the tabs and replacing it with a somewhat more functional filter is on my list. Also splitting the columns.
There is already a copy to clipboard button. It copies the address as plain text though. Why a QR code?
Another idea: In the send-dialog: When sending to an unknown address, can the user type in a string which is then included in the adressbook with the address?
Yep, I think this is a good idea