It appears that the very first place one might see a tablet computer in action, at least one looking so minimalistic as an iPad, is in the 1968 film "2001: A Space Odyssey" by Stanley Kubrick. This movie features at least one scene in which a couple of tablets are used to compute while breakfast is being consumed by their users. What this particular scene is being used for at this very moment is so-called evidence that Samsung's Galaxy Tab 10.1 tablet design does not use the iPad 2 for inspiration, that instead a single screen with little border surrounding it used for computing has been a common design for a "tablet" computer for quite some time.
The funniest bit about this entire situation is that Samsung literally attached a YouTube clip to a court case file as evidence that as far back as 1968 (in the Kubrick film) tablets have had a rather chopped-down look to them. Whether or not this actually holds up in the case is yet to be seen - what's interesting here is that by including a YouTube clip, Samsung has made this part of the case viral.
Another item of note is that the interior of the spaceship Discovery, this "tablet" scene included, was conceived several months before it was actually filmed, filming taking place somewhere inside 1965, pushing this "invention" date back even further. The officers aboard the ship, Bowman and Poole, also should be noted as using 9x16 ratio tablets, much larger than what we're seeing in 10-inch tablets today. The YouTube user septemberX uploaded this video back on February 11, 2010, so we can guess that he had no original intent on it being used for this court case.
Samsung's note includes the following:
Attached hereto as Exhibit D is a true and correct copy of a still image taken from Stanley Kubrick’s 1968 film “2001: A Space Odyssey.” In a clip from that film lasting about one minute, two astronauts are eating and at the same time using personal tablet computers. The clip can be downloaded online at http://www.youtube.com/watch?v=JQ8pQVDyaLo. As with the design claimed by the D’889 Patent, the tablet disclosed in the clip has an overall rectangular shape with a dominant display screen, narrow borders, a predominately flat front surface, a flat back surface (which is evident because the tablets are lying flat on the table’s surface), and a thin form factor.
Science Fiction always, always paves the way for the future. Though "true" Sci-Fi always shows a bleak, dark look at the future, here we see our present played out through the tablet computer. Whether or not it's actually the first iPad-esque tablet or not, we're not sure. What we can be sure of is that the idea has always been awesome.