Until now, it was only possible to get online access to vital record information for MA up until 1920.
While these databases still don't give access to the actual records-- just the indexes-- they give very helpful information, such as the name, year of the event, and where the record can be found.
There were entries for the births of my father and aunt, my grandparents' marriages (both sets of grands), and my paternal grandfather's death.
Then I found a death record index entry for a "John Woodard Howes", who died in 1933 in Cambridge, and who is almost certainly my great-great grandfather. I knew that John died in 1933, and that he is buried in New Hampshire with my great-grandmother. But when I had tried to order his death record, New Hampshire didn't have one for him.
I had guessed that perhaps he had died elsewhere, and figured either Massachusetts or Maine as a good bet. I didn't want to spend $28 on a records request to MA only to be told, "Sorry, we don't have it." But now that I'm reasonably certain that the John Woodard (supposed to be Woodward?) Howes who died in Cambridge is him, I'll go ahead and order a copy of his death record.
I also found, even more interestingly, an entry for the birth of my mother's half-brother. My maternal grandparents had divorced in 1948, and by 1950 my grandfather Henry was remarried and living in in Haverhill with his second wife and their son. My mother, who was estranged from her father and in fact never saw him again after her freshman year of high school, only ever met her little brother once. He was a baby at the time, and she told me that she remembered that he was really cute.
So I have a half-uncle, very likely still alive, whom I've never met.
It was a great idea for Ancestry.com to put the indexes up-- this provides enough information to help to armchair genealogists like me without compromising the privacy of those still living.