Well, apparently it wasn't all for show. According to the Tokyo Metropolitan University Space Systems Laboratory, the whole thing was pretty much legit...
In an article posted on their homepage, the members of the Space Systems Laboratory picked apart the 6 minute space heist in the Evangelion movie, from the basic jargon to the actual physics involved. While the giant biologically engineered almost-humans with deus ex machina-type barriers is obviously a technological fantasy, most of the rest of the space scene was not. The SSL article even describes how the movement of the jettisoned boosters was accurate.
The article goes into technical depths that honestly make my head spin. The descriptions of the speeds involved for the space rendezvous between the Eva Unit 2' and the imprisoned Eva Unit 1 made my eyes roll back into my head. Nevertheless, I was able to decipher enough to understand that 1: These people knew what they were talking about, and 2: The things that happened in the beginning of the movie made sense.
As accurate as the space physics involved in the 6 and a half minute intro were, the writers of the SSL article did find 3 inaccuracies.
1: Inside the cockpit. The entry plugs of the Evas are filled with L.C.L, a breathable liquid that helps pilots synchronize with the Eva units. While throughout the movies, the viscosity of L.C.L. has been treated as less than water, almost to be as thin as air, treating it as such and depicting the movement of things inside it as though it was not there is a little strange. Of course, this little nitpick is not exactly something that is restricted to the first 6 minutes of the movie.
2: The plume from the reverse thrust which takes place after the Eva Unit 2' makes contact with the Unit 1's coffin is inaccurate. Considering that this reverse thrust takes place roughly 100 kilometers above the Earth's surface (which can be assumed from the size of the Earth in the scene), there should be enough atmosphere to change the shape of the plume to a more rounded and thicker burst.
3: The fuel efficiency. This was another part where just trying to read it made me dizzy, but basically what it boiled down to was that considering the design of the boosters and rockets, there was apparently a more efficient way to execute the operation. (But it probably wouldn't have been as exciting.)
Despite what inaccuracies the movie had, overall it seems to stand (aside from the existence of the Evas themselves). On further research, it's been discovered that the individual Gainax went to for advice on the space scene was one Satoshi Hosoda, an engineer at the Japan Aerospace Exploration Agency who was involved with the development of the ion engine system of the Hayabusa spacecraft. I guess it makes sense that most of the space stuff was accurate.
In other Eva news, a new trailer has been released by Gainax. It's pretty spoiler heavy so, view it at your own peril.