In a few more years earbuds will be the standard 

I use Tannoy Reveal 8D's for mixing : JBL308 for jamming and general louderish playback: and Maudio BX5 and KRK 10S sub for keyboard monitoring at my keyboard rig. I'm going to re-cone a set of Altec 604's and build cabs for them someday before I croak - ( I hope). I also have a pair o Auratones - but haven't set them up yet.

I'm considering adding a 2nd pair myself.
 
A few years ago I tried out the Yamaha HS5 or HS50 (I'm not sure which) in a store. At the time I was unimpressed. I thought that they sounded "unmusical", i.e. the music playing through them was just a succession of sounds. There was no "groove". It was like it was not held together as an integrated whole. Listening was not an enjoyable experience.
 
But when I thought about it afterwards, I realised that this is exactly what I need for critical listening. When I listen back to to my projects, I often get distracted by the groove of the music or drawn in by the atmosphere, or maybe start focusing on phrasing and counterpoint. I end up forgetting to listen critically. This doesn't help when you are trying to solve problems and focus on particular issues. But taking away the musical aspect forces me to focus on things like sound and balance. The Yamahas bring out the worst in a mix and this is a good thing. I would therefore definitely go for the Yamahas as a second monitoring system.

Hence the reason why the Auratone type speaker is so good. It does not sound very good. No bass, no highs, it just lets you focus on the real important stuff and not get distracted by anything much.
 
I find once I get everything sounding pretty good on that speaker you actually do not need all the other speakers and their environments mentioned here. The mix will translate pretty perfectly everywhere.
 
You do need your main speakers up loud though to check on low end and reverbs.  There is no way around it either.  I hear that many of you cannot even monitor above 75 dB SPL or so because of neighbour issues but that sucks in reality and you will never really know how your mixes sound until you can do some serious checks at say 95 or even 100 dB SPL.  Only has to be for a short time but it is SO informative too.  That is why some of you have problems with your mixes.  You are just never hearing the LOUD mix sound. 
 
One of the reasons why people use their car is to get LOUD but most car systems are far from accurate. Although they can tell you some stuff. My car has a serious low end and when my mixes rattle my teeth I know there is too much bass. Commercial CD's have this tight controlled low end in my car. But you can get the same info up loud on your speakers too.

I carry my music to a variety of locations and systems on CDs. It isn't fast but it can be revealing.

Speaker location in the room also matters.

I'm not trying to say my way is genius or best. We all balance budget and needs. I'm only saying I have not felt the need for a second pair of speakers in my mixing space to be a priority over a nice Mic.

I got some passive Avontones recently. 
It's kind of like having a second pair of ears.

Interestingly it seems the majority of companys have shifted to the active monitors. I understand why to some extent buy now wondering if the passive setup is inferior or just more burdensome.

Well I am sure a set of passive Avantones driven from a half decent power amp would sound pretty good and not very different from the active model. It is a good choice if you have got spare amps lying around.
 
The active concept is also great too because often the power amps are designed very specifically to drive the drivers they are driving plus it eliminates the need for external amps. Also they can split the spectrum and use an active crossover and separate power amps too which can also be nice in 2 or 3 way systems.
 
I have heard some pretty stellar passive speakers driven from amazing power amps too that would in some cases far exceed active setups too. They would be expensive though.