Multitasking leads to mediocrity
I think that multitasking will need to be handled very carefully and only extended to applications that absolutely need it (e.g. music, telephony, and mail). I worry that it will increase the 'crap factor' and make the iPad less elegant and reliable.
It's important to remember that the iPad's simplicity will be the cornerstone of its success. It's really more of a consumer electronics device than it is a computer, which is why it can remain relatively inexpensive and easy to use. It provides all the functionality of a computer without the previous limitations and costs, because it has compromised certain features to keep true to its design maxim. Each app is designed for a specific purpose; form follows function. This is a nice equilibrium.
Forcing developers to keep their apps completely self-contained, as well as saving state persistence between sessions (when the app is closed, then reopened) is really good design discipline. Offering multitasking would endanger this discipline by offering kludges. Developers will get lazy and try to find workarounds, resulting in buggy software. I think that the current situation is much better.
Besides, multitasking could be achieved in a round about fashion by offloading some of the functionality of the app to a server Cloud (as ScanR does) and having the interconnectivity between applications happen there, rather than on the device itself.
No, I'm really glad that the device doesn't support multitasking. It keeps the system simple, reliable, prolongs battery life and forces developers and users to take a new, different and exciting approach to computing.