How many genres...

The imports are not divided into any genre and neither are the majority of the US releases.

I have separated about 120 albums (US) that are progressive rock, jazz rock fusion and some electronic rock.

These were the albums that I was listening to all the time so it made since to separate them.

I have most of my cds stacked in an old bookshelves thingy. Let me take a quick peak and see what's happening on the shelves closest to my bed.

Alright.

Top shelf's last three albums: Pharoah Sanders - Elevation, Michael Jackson - Thriller, Düreforsög - Knee

Middle shelf: The Cure - Pornography, The Prodigy - Experience, King Crimson - Red

Bottom: Embryo - Opal, GZA - Liquid Swords, Neil Young - Zuma

Hold on a second. All my Floyd albums seem to be gathered in one place. Hot diggity! Someone call my mother.

Neo-Prog

Prog-Metal, Metal, Post-Metal(okay anything Metal)

Electronic, Psychedelic, Krautrock, Space Rock

Jazz, Canterbury

Avant, Zeuhl, RIO

RPI

The classics of Prog which is mostly Symphonic, Elcectic as in King Crimson, Genesis

Then this big section which is like an overflow with Crossover, Eclectic, Symphonic, Math-Rock

They are alphabetical in those sub-genres. I do separate bands too. The Psychedelic period of Porcupine Tree is separate from their later period. Same with Floyd and Kraan. Bottom line is that I know where everything is which is important to me. Oh and anything I consider 3 stars or less is in boxes downstairs not organized at all, while the rest is a upstairs in the spare room.

That's purely on itunes, my cd's are straight alphabetic artist & year of release

You're right. I have over 500 CDs. They are in alphabetical order. I couldn't imagine micromanaging down to separating out Delta Blues from Chicago and Detroit Blues or various incarnations of prog into separate Symph/Zeuhl/Canterbury/Folk/Crossover/Eclectic/Heavy/Fusion bins. That's insane.

Whatever system you chose for physical CDs and LPs, be that alphabetical, by genre or by colour of the spine (yes, I've done that too) seldom works in practice because each new album you buy means you have to create a space for that by shuffling everything after it along one space to the right. That's fine for small collections but after 45 years of buying whatever album takes my fancy my collection is now distributed through 4 different rooms. This means that for a new CD that should fit say between Audience and Kevin Ayers would involve shuffling all the CDs from Ayers to Eno in the dining room along one space to the right, then moving that 'Wrong Way Up' by Brian Eno & John Cale (that I was never sure whether it should be filed under "E" or "C") from the dinning room to the living room and shuffling all the albums from Enya to Phil Manzanera along one space to the right, then taking one Phil Manzanera CD from the living room to the conservatory and shuffling all the CDs from Marillion to Soft Machine along one space to the right and then taking one Soft Machine CD from there to my home-office and shuffling all the albums from Siouxsie and the Banshees to Various Artists (WOMAD) along one space to the right... And then getting in the car and driving 30 miles to Ikea in Southampton to buy another bloody CD tower to store the overspill, where I have to also purchase meatballs and chips (covered in insipid gravy and lingonberry jam) for the whole family and come away with yet more useless junk from their "market-place" that my wife is compelled to buy, including a potted plant that we don't need that will die in three weeks from neglect and yet more sodding tea-lights (because they're 'such a bargain')... And then have to drive home with the roof down in the middle of winter since the flat-pack CD tower is too big to fit in the boot (Americans read: trunk) and because over summer I decided that a convertible car was the ideal Prog-mobile for a 57 year old gothic hippy...

...but I digress. 

I don't organise my CDs or LPs at all. I generally remember roughly where everything is, and if I can't find what I'm looking for then I have to scan the racks in every room until I find it, but hey-ho... along they way I'll invariably come across an album I haven't played in a while and decide to listen to that instead. 

If I could be suitably motivated I could in principle catalogue my entire collection (smartphone barcode-scanner + database) and record where each one was, but that presumes that they'd get put back in the same location after playing them.