I've been keeping almost any document I get (receipts, business correspondence, account statements, etc.) stored as a high-resolution PDF for about three years now. The key isn't some sort of complicated software, but rather an intelligent filing system. I organize like so...

- Year
---Month
-----Accounts Received
-----Accounts Paid
-----Medical
-----Automotive
-----Grocery
-----Employment
-----Housing
-----Etc. (you get the basic idea)

I back up to DVD-RW each week on Saturday morning after scanning in the week's documents. It generally only takes me an hour of so, and once it's done I store the originals in my file cabinet for one calendar year. For instance, on July 1st of this year, I will pull and shred the original documents for June 2005. I figure if I don't touch (or need) the originals for one calendar year, I'm ok shredding them. If I end up needing a copy, I can print it out from the PDF.

One thing that really helps me is being consistent with my file names. I generally use, for example, something like: T-Mobile_Bill_06102006_OPEN.pdf... When I pay the bill, I change the filename to T-Mobile_Bill_06102006_PAID.pdf

This seems like a ton of work when I type it all out like this, but it's really not bad. Plus, now I have one file cabinet and no clutter.

Hope this helps.