I can think of a couple of different ways that this may have been done by using a professional title application, or possibly a good photo application to create a mask that runs on top of the background video. If you were to use a photo application, you would need to then use chroma key, size and position and your favorite key frames to complete it. If you used a title application you may also be able to animate the title to get the movemenent that you want.
Perhaps the best way to find out how this user did it is to send him a private message.
I too would be interested to hear from others on other ideas on how to create this effect as it could come in very handy.
No special software required for this one - can all be done in MEP as follows:
1. On a track place your movie
2. On the next track down place the text title, white letters with a very bold font and large font size
3. On the next track down place a black, or other colour of your choice image - ensure it fills the whole screen.
4. Select the title object and from the Effects tab select Video effects, Chroma key, Alpha adjust the direction of the alpha effect - see small arrow at the left end of the title clip in image below
5. Apply any animation you require for the title using the keyframes or a movement effect.
Added: In step 3 you can also use a video clip if desired however you must be careful not to cause confusion.
Example timeline for above and screen shot of the result
You can also use the method John has described to create the kind of effect in which a transaprent ellipse (or circle) zooms in from zero to more than fill the screen. Here's an example combining both effects:
This is what the timeline looked like (apart from my music, which I added just before uploading to YT).
Note that it also works with two tracks, avoiding the need for a solid fill JPG. But you have to place the ellipse (or text or whatever) in a lower track number than the video, and reverse the arrow.