The olympic stadium is spectacular because it is one of the most notable pieces of architecture which exists not only as a structure for utilitarian use which takes on a second purpose as having a creative or aesthetically pleasing layout as its second role. It really exists as a piece of art first, and a structure for use second. I think that it's great that with new technology, we can more easily balance those two purposes. The stadium was used during the 2008 Olympic Games, a worldwide event, and took 4 years to completely put together (some of that was during paused construction time). It has the potential though to accomodate 91,000 seats. It is completely functional as well as attractive.
What's interesting now, though is that because the stadium served such a significant purpose for the olympics which were now 5 years ago, the stadium which was built to hold so much activity is somewhat void of any activity now. Tourists come and go, but ultimately the stadium is not being really put to use. Now, given, the colosseum has a similar problem, but it has been around for hundreds of years in addition to taking more than double the years of creation and serves many more historical purposes than the Beijing stadium. Therefore, it is hard to say what there is to do with these new structures that emerge seemingly so easily now. When many architects now has the resources to be an artist in their own right, it is easy to invision a world where structures like these are abundant, but when their use "runs out" so to speak, it is a hard distinction to make whether it is worth really having them stand. Of course, the Bird's Nest is in it's own right an historical landmark, but when structures are not so much is when it will become a tricky situation.