As some fans of Doctor Who have already noted, the inclusion of mention of companions of the Eight Doctor's from audiobooks in the prequel minisode “The Night of the Doctor” seems to give the stamp of canonicity to those stories.
Of course, that conclusion perhaps needs to be tempered by the fact that even the TV movie featuring the Eight Doctor is not always treated as genuinely canonical – the whole notion of the Doctor being half human on his mother's side has been set aside.
The return of Paul McGann is itself a fantastic treat. But how much is to be made of it when it comes to the details? For instance, his newer haircut and clothing appear to have been set aside altogether, perhaps in the interest of making his Doctor less dark, so that the (non-)Doctor who follows him can seem darker by way of contrast?
One last thing – as someone pointed out, the fact that the Doctor asks before taking the elixir that will let him regenerate asks “Will it hurt?” It is a great pun – “Will it Hurt?”