If you guys are really annoyed with blue shells, there is a glitch you can abuse to get rid of them. I haven't done this online, as I've seen people been week-banned, and I don't want that.
What you do, is that when you hear the Wiimote speaker yell, you start sliding until you hit a 20-50 degree sideways slope. Right before you hit it, you wheelie. This causes you to change your driving degree, and makes you head a bit more to the left that you otherwise would have. For some reason, the blue shell cannot find you now, and turns back and hits the second place.
This doesn't work on all courses, and not everywhere, but it is helpful if you don't mind semi-cheating. I have only done this a few times, as I feel it is more than semi, and I haven't checked it out in TT or WFC
Ok, another shortcut you can do on many courses. If you have Bullet Bill and jump off the course, straight in direction of another platform, he takes you there if your nose is headed there. I wouldn't count this as a glitch, but some people would.
To avoid a pow-block, start sliding, hit a 20-50 degree sideways slope, release the slide button, and start a wheelie. If you timed it right, which is fairly easy, you won't get hit at all. I don't count this as a glitch either.
How did you hear about someone getting banned from Mario Kart. All I have heard is that those who were cheating on the time trials were having their records erased.
If you don't want to do the 20-50 degree slide to dodge a pow block, you can minimize the pow block by doing a trick. All you do, is when the pow block goes off, you act like your executing a trick, and you spin once, and you don't come to a stop.
Doing that move can gain you a large lead or help you catch up if others don't perform it also. As far as I can tell, it was intentional to include that.
I don't know if hopping will do the same or even a complete dodge, but any small jump will save you from a pow block.