All those links can be very distracting. Nick gets at this point very clearly:
The link is, in a way, a technologically advanced form of a footnote. It’s also, distraction-wise, a more violent form of a footnote. Where a footnote gives your brain a gentle nudge, the link gives it a yank. What’s good about a link – its propulsive force – is also what’s bad about it.
I don’t want to overstate the cognitive penalty produced by the hyperlink (or understate the link’s allure and usefulness), but the penalty seems to be real, and we should be aware of it. In The Shallows, I examine the hyperlink as just one element among many – including multimedia, interruptions, multitasking, jerky eye movements, divided attention, extraneous decision making, even social anxiety – that tend to promote hurried, distracted, and superficial thinking online. To understand the effects of the Web on our minds, you have to consider the cumulative effects of all these features rather than just the effects of any one individually.
You can read more here. And some more below. Lets put links at the end.