I've used them, or things like them, in the past. They worked really well, and the players really seemed to like them. I'm sympathetic to the issue of vignettes giving players out-of-character knowledge, but I've found that the response from the players, and the drama they add to the game, outweighs that issue. I haven't used them more often mostly because of the prep time requirement.
Something similar that I did for my last big campaign was to run a prologue adventure. Essentially, I ran a standalone adventure set about 20 years ahead of the campaign, which set up a bunch of the conflicts that would occur in the campaign.
It did a good job setting up the campaign world. It let the players try out some homebrew classes and rules relatively risk-free. And I let the players keep the XP and apply it to the characters in the actual campaign, so the characters didn't have to start out as complete pimply-faced noobs.
It was a hit with the players, and I think it really kicked off the campaign nicely.