The problem with most personal technology these days is that it's exactly that - designed for one person to use. This is understandable if we're talking about a smartphone, but I don't think it's good enough when we're talking about Apple's new wundergadget the iPad.
If you take a look at Apple's Kool-Aid drenched iPad demo video, just about all of the demonstrations take place in the lounge room. That's understandable, because the iPad is too big for your pocket. It's a device that's better suited to the coffee table than the bus stop or your desk.
Anyway, if the iPad is going to live in the lounge room then you have to expect more than one person is going to use it. I don't care how good the iPad is, I'm not going to buy one for every member of my household. The problem is that the iPhone OS software is built around a single-user experience. It's designed to handle my email, my calendar, my contacts, my bookmarks and my browsing history. It's also designed for my apps to automatically log into my accounts for services such as Facebook, Twitter and Skype. Even if I trust everyone else in the house not to snoop in my affairs, I don't want the hassle of logging in and out of all these services every time I sit down to use the iPad.
Imagine how hard it would be for a household full of people to share one smartphone. That's exactly what we're talking about with the iPad. As something that lives on the coffee table, the iPad is more likely to be stolen than the iPhone in your pocket - so Apple might want to flesh out the iPad's auto-lock and remote lock/wipe features as well.
There are a few workarounds for the iPhone OS that would make sharing an iPad less painful. The iPhone email client will check multiple email accounts, although anyone who uses the iPad would have access to every email account. You could use a combination of Mobileme and Google Calendar to access multiple calendars at once. With a bit of tweaking you might be able to merge address books as well, although it's something I've never attempted.
The new homeshare feature in iTunes should let you copy content from several iTunes accounts onto the iPad and there are even ways to transfer apps between iTunes accounts. Of course the real hassle is not the price of the apps, it's the user data. I'm talking about login details, in-app purchases, games high scores and other user preferences. All that things that make it my device.
I can understand why Apple has never bothered with user switching on the iPhone, but if it wants to inflict a smartphone OS on our lounge room then it really needs to add some extra flexibility to the iPad.