Well I can't really see what benefit Apple would get from entering the PDA market. I know that this has been a long rumored item, but I am stuck as to what this realistically might be.
Witness iSync to show that Apple already consider the Palm OS devices the standard in PDA's. Unless they had a compelling advantage to offer the mobile business community, why would they want to create "another" option for people beset by Journada's, iPaqs and Palms?
Steve Jobs has already mentioned, and I have to agree, that for most intensive tasks, a full computer is needed (full size display, full size data-entry device - keyboard). The only way I see Apple entering the PDA market is if they've got something killer like a foldable display or decent voice recognition - both of which are still some years off (for portable devices anyway, I KNOW that MacOS already has VR). But you only have to look so far as the Newton to realise that people use any given device for its functionality - no matter how cool the technology underneath is. People marvelled at how amazing the Newton was, laughed after watching it interpret a few handwritten words, then put it down and walked away (except me, who still uses a 2100)
At the end of the day, most people don't need a spreadsheet on the move. For those that do, there are already good solutions.
To further elaborate on the home-device described before, a hardware QuickTime Player would be THE linking unit that would ultimately make your living room a peripheral to your Mac. This furthers the Digital Hub design, with the Mac at the center.
The "CPU" of the device would be only for media playback. You would still need a Mac to load it up with its content. With no direct net access (unless it's got a built-in browser, but that gets WAY complicated and might as well become an iMac/eMac) you would need a Mac to download stuff from the web, mp3 stuff, etc.
Think of it: on your desktop you've got the icon for this device that's airported from your living room. You can drag/drop whatever files you want into it, then go into the living room and watch the latest trailers on your big screen tv - or listen to your mp3's through your home stereo, ultimately using the box as an mp3 server (see iTunes 4 functionality).
This device, based on QuickTime and open standards, would be (once again) a unique market. To my knowledge there is nothing that exists today which it would compete with. Competition would have to also be based on a QuickTime architecture, which means that Apple would always have the advantage when it comes to Mac integration. Perhaps Microsoft will eventually come out with a similar product, but with .wma and Windows Media Player compatibility, but then who would care?
I think the key to this is turning your television and stereo into a peripheral of your Mac. Once that happens, Apple will have completed the home-invasion and will next have to line up the Apple-branded toaster (FINALLY!)