I've been using the ipad since it launched, I've saved hundreds$ on paper, but I always keep a very basic receipt book with me (I newer use it) just in case I get older customers that don't have an email address.
The best program for me is Invoice 2 Go. They have come a long way since they came into the industry. They have apps on iphone, ipad, android..
There are 2 versions for iphone and ipad that im aware of... you can sign up and pay a small monthly fee and you get cloud backup with it or you can buy the app for a 1 time fee, and manually back it up as you see fit (super easy), then there are in app purchases that let add on other things like, sign2go, statements2go, receipts2go, calendar2go, scan2go, and maps2go. I have them all except the maps2go & calendar2go, and the only one I don't use is scan2go, it's more for those that have actual products with bar codes.
If you're seriously considering getting away from using paper, this app in my opinion is the best one that allows you send out Invoices, statements, Estimates, Purchase orders, Credit Memo. Only thing they're missing is the ability to process cards within the app, but they do have a function where you can put your paypal email in and when you send it out, it has a paypal button at bottom that your Client/Customer can click on and pay you, and they don't need a paypal account to pay, pretty cool feature for those that have a paypal account
I just signed up for QuickBooks Mobile, and it does a lot of the same stuff, but it doesn't allow signatures (for credit card processing only) but it's quickbooks and you can manage things more seamlessly with bookkeeper/CPA.
ATX