Basically, you do text in Blender, immediately convert it to a mesh. Now you go into edit mode and extrude it...but click your mouse immediately so it doesn't actually extrude, this gives you, in effect, 3D mesh text that has been "squashed" perfectly flat with all the verts for the front "face" selected. Without changing the selection, go into object mode
In object mode, you set a shape key to this base shape. Now go back into edit mode, grab and move the verts straight out from the lettering. The default for adding text is in top view, so, if you are in top view, just do G-key and then hit z and you can grab the verts and move them up in z. Basically this is the same as extruding them. Now, while still in edit mode, set another shape key for this "extruded" shape.
If you go back into object mode, you should be back to having 2D looking text. But if you split up your windows and make one of them an Action window, you should have a slider for your second shape key. If you move the slider, your text will extrude. From there it is a simple matter of making an animation.
However, for the example below, I took the further step of animating the mesh moving toward the camera after the extrusion of the shape key. It works like this, for frames 1-30, the text mesh is in the same location. On frame one, it is at the base shape key, i.e. 2D, I go to frame 30 and move the slider for my second shape key all the way, now, at frame 30, the text is "extruded" all the way. So if I animate, it shows the text gradually extruding for 30 frames. Then, at frame 30, I start the mesh moving toward the camera until it goes completely past the camera at frame 50. Below is what you get. The text is done with the Precious Materials pack (link off the main Blender.org site), with the silver material tinted blue and some transparency added.
You could also start from the opposite end of things and have the text "zoom" past the camera and go from 3D to 2D. Another thing to try would be to use a "zolly" style shot. I have experimented with these in Blender. What you do is to zoom and move the camera at the same time, trying to keep the subject centered and the same size in the frame. What this does is to cause the perspective to seem to shift around the subject. It is a very unusual effect. If you don't know what I am talking about, if you have seen the first Lord of the Rings movie, the technique is used in the first part of the film when Frodo, Sam, Merry, and Pippin first encounter the Nazgul. The four of them roll down a hill, then land on a road bed. All of them except for Frodo immediately start investigating a patch of mushrooms. Frodo is uneasy and looks down the road. The Nazgul is coming and we see the "zolly" effect as Frodo realizes something is very amiss....
