Um, how about "don't do that"? With serverless storage engines like SQLite3 around, there's no reason to fool with trying to read/write everything to a CSV file.
--Matt Jones
I'll second Marnen's idea.
With a DB you'll get random access to any record. Using a CSV you'll either have to read record by record until you find what you need or dump everything to an array or hash and then get it from there. I think it's actually more work going the CSV approach.