Hello!! I'm a May 2010 bride too. :-)
I just thought I would share our strategy for saving some $$$ on invites/STDs!
We created a wedding website (through brides.com) with all of the details about the wedding, plus everyone will RSVP on the site too. (I had friends who did the same thing and said only a couple of relatives didn't have internet access, so they just called to RSVP and they updated it manually.)
We were originally going to send out save the dates, but realized that they would say the same thing as the invitations (since the RSVPs are online, along with all of the details, there was no need to do the formal invitations with all of the enclosures). So, we decided to send the invites now, even though it's early. That way, people have even more time to plan and save some money if need be. (I'll post a picture when they're done - we went the DIY route too to save even more $!)
So, basically we cut out the cost of save the dates, the cost of RSVP cards and postage, and the cost of multiple invitation pieces and expensive printing. Plus, we both are pretty environmentally conscious, so we were happy to be able to save a few trees in the process. (And some of the paper I am using for the invites is recycled.) YAY!
Oh, and we went on godaddy.com and bought a personalized web address to use on brides.com so it would be easy for people to remember the site address.