I understand dealing with May 2009!! I already have the villa booked where we'll be having the reception and staying (along with our immediate families and close friends) and the date is set in stone. Airfare cannot be booked until 330 days before the flight, but I'm not worried about that. Flights to St Lucia don't exactly fill up the first day. We're actually ditching the STDs and going for super early invitations. I hate how invitations just turn into a formality. If people need to know 10 months in advance so they can plan according, then I'm going to invite them 10 months in advance. I know many probably disagree with me on this, but if I'm going to work really hard on boarding pass invites, I want them to be more than just a formality.
Oops, sorry for the rant. Anyway, back to the point, I wouldn't bother sending out a save the month. I would wait until you have the actual date--and it's definitely not too early to set that. Don't let people make you think it is. And feel free to send out STDs as early as you want. No harm in that!