Okay, so some time today, the Apple Tablet is going to be announced. That much seems certain. Everything else is a guessing game. And 'game' is the operative word. It's a game that's being played by every newspaper, many bloggers, and even has its own scorecard. Games need players, and I don't like to be left out, so here's my attempt at guessing the device:
Name: Mac Touch. The thinking behind this is that apple doesn't like to introduce too many neologisms, and "Mac Touch" positions the device between the iPod Touch and the Macbook - perfect, because the tablet is designed as a "gateway device", targeted at those who have iPods and iPhones but don't have a Mac (or even a PC) - and there are a lot of these people, believe it or not.
Operating system: Based on the iPhone, but with some added features that make it more like the regular OSX. Namely, Apple will finally have figured out a way to allow apps to run in the background, whilst maintaining performance and battery life (perhaps by some kind of special sandboxed 'standby mode' that gives apps limited abilities to run a set number of processes in the background, such as downloading, playing audio, or updating a web server at a set interval). There will still be no file system - instead, applications can save files to one of several 'buckets' (eg Photos, Videos, Audio, and a new PDF/text/ebook app).
Hardware: I'm not going to bother to try and predict the exact screen size or dimensions. However, I do think the device will be notable for having no hardware ports at all. No USB sockets, no headphones socket, no display adapter. The only thing you'll attach to the device will be a power cable. Everything else will be wireless. The device will have a camera on both sides, and the screen will be some sort of glare-resistant, low-power, read-in-daylight screen, but in colour. It'll have Wi-Fi and mobile data access, but won't bother with Bluetooth, infrared or RFID (as ad-hoc wi-fi networks render these mostly redundant). There won't be a hard disk either, just solid state memory.
Apps: I think the tablet will mark the point where Apple does a bit re-jig of the iTunes/App Store system. The store will get moved out of iTunes, and will become an app in its own right. Video will move out of iTunes and into a new iPhoto app. There will also be a new app that manages text-based documents (magazines, newspapers, books, etc). The App store will be integrated into all of these. However, Apple will also allow direct download and purchase of content via third-party websites (in answer to criticism of the perceived monopoly) - however, the user experience won't be as good (as you'll have to re-register your credit card, etc), and Apple will rely upon this (and its library and pricing) to maintain a good market share of the digital content market. Applications can be installed from other sources too, though they come with lots of warnings and disclaimers that you have to click through. The iWork apps (Pages, Numbers and Keynote) won't be supported, although you will be able to view the outputs from those applications (documents, spreadsheets and presentations).
Other: They'll announce some deal so that people with an iPhone can use the same contract and data plan across both devices. You'll finally be able to sync iPods wirelessly with the tablet (and regular Macs). You'll be able to 'subscribe' to magazines, TV channels/networks, and other content streams, which will give you unlimited access to download or stream their content. Crucially, if you unsubscribe, you'll be able to keep any content you downloaded, you just won't get any new stuff.
And there you go, I'm done. I have to admit, the predictions are based more upon what I'd like, and how I'd design it if I were in charge. But if Apple are as much of a genius as me, then I'll be at least half right... :-)