I've been aggressively moving everything paper over to my iPad with pretty good results.
For Magazine subscriptions, I use Zinio. I have about 20+ subscriptions that sync over the air directly to my device. It's such a pleasure not to have to use iTunes to do this! After some teething troubles - and frequent crashing - the Zinio team have made a stable application that is improving all the time. Over the last couple of weeks, it has been given a speed increase - although, scrolling magazine pages is still a little slower than I would like. Zooming in on a page is also a little delayed... but not unbearable by any means. I have already downloaded 52 magazines to the device without problems so far, so I am impressed.
For Newspapers, I use PressDisplay. I don't know why more people don't know about this, because it's absolutely incredible. 1500+ newspapers delivered over the air to the iPad in their original format. I have chosen to have 5 of my top favourite newspapers sync on a daily basis. It's a pleasure to crack open the iPad on my commute to work and read the broadsheets - as they were meant to be read - in full fidelity and in colour. Cleverly, they avoid the whole zooming in and out delays by allowing you to click on a mast headline, which results in a text pop-up (with pictures) of the article that you can scroll through. Turning pages is surprisingly fast, given that amount of information that is being processed. You can, of course, zoom in on the page if you like but it's not necessary.
For Documents, I like ReaddleDoc. It handles Microsoft Word, Excel and Powerpoint files pretty well, although there are the occasional discrepancies with diagrams in powerpoint. However, it's really the PDF handling that I think is the most exceptional. I have thrown various different types of PDFs with different compression settings at the application without any probs so far. I have tried Clearscan and the latest Adobe 9 formats. I haven't yet tried JPEG2000. The app also connects to Internet shared folders and servers extremely well, in addition to MobileMe's iDisk.
I have scanned a lot of books and moved them to my iPad. Yes, I have both Stanza, iBook and the Kindle app - but not everything is available in a digital format. I bought a large guillotine cutter and I have been scanning my library of favourite books. It's sad to have to cut these books up but this is outweighed by the pleasure of having them on my iPad to read anytime, anywhere. I put them on a folder in the MobileMe iDisk, so I don't have to load them all on the iPad until I'm ready to read them. I've scanned 134 books so far and roughly 340 magazines... so, it's turning into quite a back catalogue. However, Clearscan compresses things like a dream and the text in these documents is full-text searchable.
Onwards and Upwards...