My wife and I have been keeping a check book by hand since 2004 when we where married. We would like to start using a piece of accounting software (GNUCash) to track our finances instead. How far back in time should I enter data into the program? I tried to go back to 2004 but the task seemed overwhelming.
As others have pointed out, now is the best time to start. I would suggest writing down all your open checks as they stand right now. And your current balances. Put these in the software as your starting position. For anything earlier you can refer to your existing notes, for anything later just keep entering in Gnucash and you'll be set.
A word of advice; backup, backup, backup. Computers are great but paper has the perfect advantage of being automatically saved. I usually backup every week in a separate file and then copy these over to a hard drive every month or so. I use Kmymoney and it has a menu option to take backups. I'm sure Gnucash has something like that too.