I have changed my down-pointing tailpipe to straight-out. 2 things gained : (1) it is smoother and responsive (2) nice looking (hehe...)
I saw a black 320D changed to straight-out the other day at eat-west highway. I give 2 thumbs up :-D
AHMZ, if you were to floor the gas pedal at traffic light or anytime while driving, with down-pointing tailpipe, the black smoke is significant too..... so change or not change the black smoke still fart. But, one thing you may want to take note is - wash frequently especially those driving light color 320D.