The maker and claimed "pilot" of the construction now has outed the whole thing as an hoax on Dutch TV and made an official statement on its website http://www.floriskaayk.com/:
Today, I revealed my latest project on Dutch prime-time TV show 'De wereld draait door'. In the past months I have been working on an exciting fictional online storytelling project called Human Birdwings . To be precise, Human Birdwings was an online adventure and invention story in which fictional character Jarno Smeets developed wings in a do-it-yourself manner
The following websites mentioning it as well:
Gizmodo: Flying Bird Man Admits Flying Bird Man Is Fake
You're looking at the Internet Bird Man, who captivated the web's attention for dozens of hours and divided us between skeptics and the faithful. It was a hoax! It turns out he even made up his name.
Jarno Smeets—actually a Dutch CGI artist named Floris Kaayk—fessed up to the hoax on De Wereld Draait Door, a Dutch TV show.
Mythbusters (some link as below, now edited):
Editor's note: "Jarno Smeet" has gone on Dutch TV exposing the entire affair as an elaborate hoax. I've updated the headline to reflect. More details to come soon.--WS
update: It's a hoax. The Internet Bird Man fessed up to the hoax on a Dutch TV show. It turns out he even made up his name. Jarno Smeets is actually a Dutch CGI artist named Floris Kaayk.
Since the recent publication of the "success" video there have been several responses on different websites. Through them I'm actually now able to give a referenced answer myself.
There are some people with technical expertise which note that it seems to be technical possible, and does not need to be a fake on technical grounds:
Jamie Hyneman (Mythbusters): Thoughts on The Mechanics of Assisted Human Flight.
Rhett Allain, Associate Professor of Physics at Southeastern Louisiana University: Analysis of the Human Birdwings
However the following news and science/technology websites have reported it seems to be a fake either by themselves or by quoting experts:
Fox News: Viral 'human bird wings' video fake, probably an ad, expert says
Wired Science: Bird-Man’s Resume Doesn’t Check Out: ‘Nobody Knows Him’
Gizmodo: CGI Experts Say Flying Bird Man Is Fake (taken from John C's answer)
Gizmodo: Man Flies Like a Bird Flapping His Own Wings
Science on msnbc.com: 'Human bird' video flying high, but experts say it looks fake
Gadget Review: Fake: Human Birds Wings (video)
Apparently there are some clear hints about CGI techniques used for the video(s). Other things like missing load on the wings have been pointed out. Also the background story of the pilot does not check out.
Some (in the above linked posts) assume that this is meant as a viral ad video for one of the companies which products were used by the project, like Nintendo.