This is indeed album number 5! She announced it a few months back. Here is the thread with all we know so far:
http://forum.nessaholics.com/index.php?topic=13434.0It is yet to be seen if this is purely a V project or an expansion on the electronic side project she said she began plotting with Steve the last time she was at Real World, when she mentioned "Moneymaker". Whether "Euphoria" is the name of the album or the project isn't clear, but i'm confident this will be a Vanessa Carlton album.
She mentioned a year ago a new song about a ghost in a lighthouse or something? And then tweeted about "a song idea like a cinema". Then recently she has given teases of new songs "Patience" and "Take it Easy", and mentioned that she has been quite in a productive space with her songwriting.
That pretty much brings us all up to speed!