"truck swung at green martians are heavy."
I really like the way you presented the instructions on the opening screen, though I wasn't smart enough to read them before plowing ahead into the game. =)
The shiny letters are definitely easier to pick up than the dull ones. Once in a while I wanted to force a word so I had to go outside the highlighted letters. It was pretty hard to "collect" the dull letters because they really wanted to jump out of the viewport at the last second--lots of arrow key fiddling required. The shiny letters were a little hard to see before you got close to them; maybe they could have borders, or appear in front of the shininess, or the shine could pulse on and off?
It would be cool to see that "probability this is English" percentage. Maybe the higher the percentage, the faster you fly? I agree with moonmagic: having a time limit or a character limit would help define a goal. Maybe there could be powerups or obstacles (asteroids? wordsteroids?) in the 3D world, too.