It is pretty standard vampire lore that in order for a vampire to be able to come into a home or even a town, they have to be invited. In 30 Days of Night, however, I don't remember there being any sort of invitation and the vampires seem pretty free to come and go into the houses and the town as they please.
I'm willing to accept that not all vampire tales have to follow the same rules, and in fact there are many differing aspects to them such as how they are affected by sunlight. Another traditional theme however that 30 Days does comply with is that the vampire(s)' coming tends to be preceded by a human thrall who is sent to prepare the way for them (Renfield in Dracula, or Ben Foster's character in 30 Days).
So I'm curious if the "invitation" element was simply omitted from the 30 Days version of vampires or if I just missed it somehow.