In an excellent article Robert Cottrell makes a smart point about online writing:
It helps, too, that when you’re writing online, there’s no need to introduce and source every person, place and fact you mention, and no need to fill in the backstory for those new to the subject. You can link out to the source document or the related story – or just assume your reader knows how to use Google and Wikipedia.
It is very annoying to read articles that have too many hyperlinks. I think a thumb rule for hyperlinks should be: use no more than 1 hyperlink per 200 words.
PS: In case you can’t read the linked FT article, try this.