For me, it was bid proposals. Lots of them.
A small but really annoying part of my job involves sending out
RFPs for purchasing big ticket items that can cost a lot of money (petabyte storage systems, lots of servers, large amounts of fiber and networking gear). You send out a document to all these companies telling them what you want, and they come back to you with a proposal and a bid. Then you sit in a room with a bunch of other people working on the same project and figure out which of the proposals you want to go ahead with.
Sadly, this process relies on paper, and lots of it. You send out RFPs and get back
these gigantic binders that are heavy and full of paper, and weigh a ton. It's often so heavy that I once had a stack of these for a project on the passenger seat of my car, and the car started beeping to warn me that the "passenger" didn't have their seat belt on.
That heavy.
One day, I got fed up. I had skipped the original iPad because I already had an iPhone and didn't see the pint. But then the iPad 2 had come out, and I was looking at its specs. It can do PDFs and is super light and easy to carry. And we have a bulk scanner, which can take all those thousands of pages of paper, scan and OCR them so they're searchable, and make PDFs out of them.
So, a couple days later, all my co-workers were lugging in their stacks of binders, and
scowling at me as I laid down my light little iPad 2 and easily flipped through documents and searched for pricing and other figures. At that point, I fell in love with it. Since then, a lot of my co-workers have bought iPads too, and we try to stress to vendors that if they send us a proposal, we'd
really like it if it was sent in PDF or some other tablet-friendly format, and some are glad to comply.
I still use my MacBook air for lots of things, but anytime I want to just do e-mail, or look up some info, or just mess around on the couch at home, it's the iPad I go to. when I want to read something, all I buy are eBooks now, pretty much. The iPad 2 is long gone, but I have an iPad Air now, and my significant other is happily using the iPad 3 Retina I had before upgrading again.