I just missed the clean finish bonus because the grid wasn't cleared

[Stellar Jetman]

Would it be acceptable to add a few seconds of silence to the end of the song in Audacity or a similar program?  Or would that be considered cheating?

It's only natural that you see this differently than I do, however does this "rule" really add to the depth/fun of the game? I don't think it does.

Exactly.  Difficulty is good, but it should come from overcoming the obstacles in the game, not from having to compensate for the engine's deficiencies.  Bad collision detection or laggy input would also add "difficulty", but is that the kind of difficulty that a game should have?  Of course not!

[blue_h3x]

Changing the song would count as cheating. Although depending on the song there can be more than one in popular circulation, often due to single, album and compilation versions; manipulating the song length to boost your own score is cheating.

If a song was of length x, but your one score showed x+2 as the length, then you might just get called a cheat for it.

Collecting the last block just as the song ends leaving blocks on the board, should mean it wasn't a clean finish. Collecting the blocks such that the last match clears just as the song ends it where the skill lies. Unless your computer is fairly low spec, the engine's lagginess shouldn't be an 'obstacle', though Quest3D sure has it's issues sometimes for no apparent reason. So I'd agree with aeminence here.

[Laserrobotics]

It's not a deficiency of the engine, it is simply a special case that has not had much of anything done for it.  The blocks wouldn't clear normally because the song is over; time has stopped.  Likely the reason that it still doesn't go all the way with it is that some people have argued for the keeping of this mechanic.

[Cadiuro]

I don't know what you guys do, but when I'm playing, I barely watch my board - I'm watching the lanes a while ahead.

Anticipating what you still can or can't grab is in my opinion a part of "skill". Agreed, this can be though on a fast, abrupt song, but the first run is almost never a good one, isn't it? If you know the ending sucks, you can expect it in your second run and act accordingly.