- since a genre is a name (imo), shouldn't all be in capitals ? i.e. Canadian Blues instead Canadian blues ? Another subjective bit probably... 
It's probably a personal preference, I think it looks better.
And to me it also indicates the name is taken to be as just some label name as a whole, and not every word has meaning.
What I mean by that is:
'Country pop' is considered to be Country, not Pop.
'Acid jazz' is considered to be Electronic, not Jazz.
'Dance-punk' is considered Rock, not Punk.
When pop, jazz and punk would be written in capitals here, it might give the impression they have more importance than just being part of a name.
So I chose to be consistent in only capitalising the very first letter of genre names and not give it much more thought.
- I would definitely split Pop from Rock
I can understand that, but I decided to combine Pop/Rock as a main category because for most of the music I know that falls in the pop and rock categories, it would be a difficult and very time-consuming task for me to determine if I consider songs and albums to be either pop or rock.
And I don't want to waste too much time on details that don't bring me much benefit.
If I have music I strongly feel only fits one of these genres, I can easily add either Pop or Rock to the tag.
So initially all my songs and albums in these categories have 'Pop/Rock' as a genre tag.
Then as a start they will all conveniently show up when I select the Pop/Rock category.
Then the ones I have stronger opinions on will have: Pop/Rock; Pop and some will have Pop/Rock; Rock
For me this is best of both worlds, it's easy to use, and it allows for whatever pop/rock filtering you like.
I use a similar method for genre categories. Lots of my music I am not sure of if I should put them under Pop/Rock or Electronic.
I will then just tag them with both the genres Pop/Rock and Electronic, so they will show up in either category.
Fine tuning can be done later, but I want to be up and running as fast as possible, and with the least amount of effort.
This sheet is about being practical and making things easier, without simplifying, dumbing-down, or being plain-wrong in certain areas, and I feel it does that rather well by now.
And it's very easy for users that have different preferences on categories to just make some changes to the sheet and do some relocation.
updated (v0.98)
- made some improvements here and there
- added Non-music as a category
download Genre-Subgenre sheet