Former NASA astronaut Edgar Mitchell says yes - we have been visited. The interesting question to me is… how long could X people inside the government, NASA, etc. keep a secret like this before credible evidence from a credible source comes out? The key would be keeping a lock on the evidence, so without simultaneous confirmation from a large group of insiders each leak looks like a minor kook.
Update: here are the pictures: http://www.news.com.au/gallery/0,23607,5029118-5007150-1,00.html
From your link, I clicked on the photos of UFO’s and they are very convincing.