Android is a bit limited for programming right now, due to lack of IDE's (I only know of one, though there are some editors), and programming is also more comfortable on a larger screen, but I think that in practice it's not that bad. I've programmed on a Fujitsu P1510D, an old subnotebook with a 1024x600 8.9" screen. Wasn't a lot of fun, but was workable. An android PC could be easily constructed that's better than this. For writing there's a lot less problem, IMO. (I'm a programmer and have also done some writing, including on a Psion Series 5mx.)
(And really, when I'm multitasking a lot while programming it usually means that I'm doing stuff that's not related to my work. So limiting multitasking may actually be beneficial.

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Multitasking on a PC starts becoming really different when you have more than one screen. That's something that Android can't compete with at this point. But I don't feel that there's a huge advantage to Android if compared to a Windows device of the same form factor, in terms of multitasking. I regularly switching between e-mail, browsing and reading on my Nexus 7.