Unfortunately some of Midnight Sun was leaked online by someone Stephenie Meyer trusted (she gave several mauscripts to close friends - each one with subtle differences). She has even gone so far as to say that this breach of trust will make her discontinue writing the companion book. However, she has put the leaked version for viewing on her website in order to make fans not feel guilty about looking at the leaked one. She says it has a few spelling errors and such but you'll be happy to know it's a staggering 264 pages so far.
View the manuscript here: http://www.stepheniemeyer.com/pdf/midnightsun_partialdraft.pdf
The message from Stephenie can be seen here: http://www.stepheniemeyer.com/midnightsun.html