The Hitch Hiker's Guide to the Galaxy contained as much information as “several inconveniently large buildings” – but displayed it on a four-inch screen above hundreds of small buttons. Were Douglas Adams writing today, he might have imagined a touchscreen tablet. Certainly the entire consumer electronics industry seems convinced they are the future – inspired both by Amazon's Kindle e-reader and the expectation that Apple will today launch an iSlate/iPad/iCanvas. But in spite of all the hoopla, there are reasons to question tablets' promise.

Consider netbooks. Taiwan's Asus (egged on by Intel) discovered a market for small cheap laptops and competitors noticed the demand. First launched in 2007, about 29m were sold last year, accounting for two-fifths of the laptop market. But computer makers have flirted with tablets for decades without sparking mass-market interest.

The importance of eye-catching technology can also be overstated. Apple's iPhones are popular and very profitable but they accounted for just 0.2 per cent of the 1.1bn mobile phone units sold globally last year. Amazon has yet to disclose how many e-readers are out there.