The storage density of A-format mass market paperbacks containing dense UTF-8 text is roughly 4Mb/Kg. (A 400 page novel weighs around 250 grams and contains roughly 1Mb. Source: I went and weighed one of my novels, of known word count.) We can up the density somewhat by bzip2-compressing and then uuencoding (or similar); maybe 10Mb/kg is achievable.
Normal A-format paperbacks use acidic wood pulp for paper, but acid-free paper doesn't add a whole lot to the cost. So we get roughly 10Gb/ton, and the whole kaboodle comes in at roughly 500 tons. As the density of wood pulp is close to that of water, this approximates to a 10 x 10 x 5 metre lump. Quite a large time capsule, but not unmanagable :)
However. If we posit the availability of decent optical scanners in 50 years' time, there's no reason not to go denser.
We can print the data as a bitmap at 300dpi and be reasonably sure of retrieving it using a 2400dpi scanner. Let's approximate 300dpi to 254dpi, and call it 10 bits/mm. Printed on reasonable quality acid-free paper, we can get 100mbits/square metre, and that square metre will weigh around 80 grams (it's 80gsm paper -- same as your laser printer runs on). Call it 1.1 mb/gram. At this density, we can print the whole 5Tb (or 40tbits) on just 40 tons of paper, without compression; with compression, call it 20 tons. That's a 2.71 metre cube; just under 9' on an edge.
This assumes a monochrome bitmap. If we go to colour and use archival-quality inks we can probably -- conservatively -- retrieve one bit each of red/blue/green per dot, and it's probably not unreasonable to expect to get a whole byte out in place of each bit in our mono bitmap. So we can probably shrink our archive to roughly 2.5 tons of paper -- a pallet-load.
I wonder if anyone has actually attempted this and seen how dense you can pack it and reliably recover. I imagine you would need measures to counter small misalignments when rescanning and imperfections in the physical media.
I've tested it out myself, and it's only after you start to crumple it together that it stops working. I tested it with an inkjet printer though. A laser printer may stand up better.
