Russell Buckley writes in Mobile Myth Busting

The myth in this case is that it’s hard to input text into a mobile phone. It may well be for you (and it certainly is for me, though my fingers nearly fly over the qwerty keyboard on my Nokia E61). But to anyone who has actually grown up with a phone, that’s simply not the case.

I fully agree here with Russell, the digital natives or should we say the mobile natives are definitely much quicker typing than we are. However, Russell's conclusion:

So if you’re thinking about launching a mobile website, as an example, and you’re agonizing over a URL that’s “easy” to input on the mobile - really, don’t worry. It’s about as important as whether Santa gets gored to death by Rudolf this Christmas.

is quite a different cup of tea. Already in the comments, Riaz pointed out that it's a completely different thing to type an SMS (intrinsic motivation and you decide how long the message will be) then to type in an URL to get to a mobile site (the fact of typing in is a hurdle and out of your control).
On mobile you are also expecting to hopefully find something interesting as changing for something else is not desired.

So I cannot agree with Russell here, typing in URL's and being sure that they are mobile-compatible (for money but also for time reasons) is still one of the biggest hindrances regarding the take off of the mobile web.
There is a solution and it goes like this:

• QR Codes for easy retrieval of sites
• Mobilized sites, pages under 30-40KB (i-modes 10KB is a bit strict today) with the exception of 3gp videos.
• A label or .mobi or anything else that communicates clearly that a site is optimized for mobile devices.
• Portals or directories of mobile sites

Someone said recently (was it Jan?) that on the web we are looking for the gems in a vast amount of material, whereas on the mobile we are looking for the diamants in the gems. I think that pretty much sums up the difference.