If you have access to Adobe Acrobat you can also photograph or scan cards, then convert to searchable PDF with OCR.
The simplest solution is to maintain a text file called, for example, addressbook.txt, and type the essential contact information. Enter new cards as you receive them, alphabetized or sorted however you prefer. Or, the text file could simply be a list of the people and the filename of the scanned/photographed card. This saves typing but adds time needed to retrieve.
A Dropbox folder containing the photos/scans could keep them handily backed up and available.
Then no OCR is necessary, and it's not easy for the system to fail.