Wow!
I had this whole huge response to this thread yesterday and my browser ate it so I gave up, but I HAVE to say something now. Not to knock the Mackies (I've got a set of the 824's myself which I love), but they do have a couple of weaknesses.
The first is that their tonality tends to change with volume. You're not supposed to vary your listening level when you mix anyway, but it's still something to be aware of. If you've got something with a lot of bass, you need to turn 'em up a bit before you can really feel it. Once you set them there, it's fine, but you need to find that "sweet spot" and for me, it was louder than I normally listened to music. And if you live in an apartment complex, it may be an issue with neighbors if the walls are very thin.
Also, if you like a very forward speaker in the midrange,(ie NS10s), then the Mackies may be too light on the mids for you. By comparison, the KRK V8s are MUCH louder in the mids than the 824s (and WAY louder than the JBL LSR28Ps). I only mention this to emphasize that you HAVE to check 'em out, at least in a store with multiple sets of speakers. It's worth a $200 weekend trip to get to a store that has many sets to try out if you're gonna spend $1500 US on something. You may find that a much cheaper speaker sounds better to your ears, or that the difference between, say, the 824s and the Event PS8s is not enough to warrant paying the extra money. Please do some critical listening, I'm begging. You'll have SO much more fun if you know you picked the best speaker for you.
Lastly, I did a side-by-side with the 824s and 624s when the 624s first came out, and I honestly couldn't hear the difference! So why'd I spend an extra $400 for the 824s? I'm gullible, pure and simple. "Why it's 2 louder, isn't it" to paraphrase Nigel.
Again, my simple suggestion - get thee to a music shop! Bring a buttload of CDs and try every speaker in the joint. My guess, you'll make multiple trips. It took me 2 years to make a choice! Oh yeah - and keep mixing. The more you can hear the individual elements of a composition, the more the differences in speakers will stand out.