I was about to post until I read this. You read my mind. Also, to lump all MBC's into the same bin is careless. The Waves L3 is much different from the RN Dynamizer, which doesn't even resemble the Endorfin. I use all of em, usually for different purposes, and not always on the stereo buss. It was right to tell the OP that this particular problem is better solved by other means, but come on... it's unfair to attack a mere tool unless it's one of those ass hats from The Real World. And considering all of the other things holding your average home recordists back... it's very trivial.
I use the Dynamizer all the time myself. Technically it's NOT a multi-band compressor...or should I say it is to MBCs what a parametric EQ is to bass and treble controls.
But that's not the point. Neither is it the point that MBCs are bad. They're not. It's their misuse on the 2mix as a substitute for tracking and mixing that is the evil, IMHO. And in my experience, it's not a trivial matter when it becomes a real trend and internet reality that that is how things are supposed to be done.
Hell we had a thread here just a few days ago, I forget which forum, where they guy was basically asking, "OK, I'm done mixing and mastering; now it's time for me to actually make it sound good it with the multiband compressor. How do I do that?" And that is far from an isolated instance. There seems to be a wikiality that has spread across the Internet like an arson fire in Greece that says:
"Here's how you make a gold record:
"1. Record using as many tracks as you can fit into your interface. Don't worry too much about the sound unless it's your guitar, then you just need to make sure you have it too loud and too distorted for actual recording, the rest will be fixed later. That's called 'tracking'.
"2. Then, individually make each track sound as good as you can get it (the word "awsome" is usually used). Compress the tracks. Pan them hard left, center and hard right. Then layer them on top of each other in your DAW software so they are all at the same volume and sum them down to stereo. That's called 'mixing'.
"3.Then apply heavy MBC to the 2mix to get it to sound right; and squeeze the results through a hard limiter set to hammer and anvil mode to get it to sound loud. That's called 'mastering'."
The only thing gold that comes out of that formula is the liquid that runs down the pants of those that have to listen to the results.
It's not the MBC's fault.
G.
I agree that the differences that exist in the various implementations of the"MBC" can make a huge difference. I tend to prefer those that use crossovers and gentle slopes ( on the odd occassion that I use them). The sonoformer is a good one . 
) that can make up in mastering for lack of technique in tracking and mixing. 
