I'm currently on:

@Computer
- Write
- - Outline
- - 1st Draft
- - 2nd Draft
- - 3rd Draft

- Listen

- Watch

- OSX
- - Mac Pro
- - MacBook Pro
- - Server

- Windows

- iOS
- - iPad
- - iPhone

- Software
- - Filing
- - Processing Retouching Photoshop Lightroom
- - Testing Lightroom
- - Mindmaps Diagrams
- - Word Excel iBank
- - Quickbooks
- - InDesign Scrivener
- - Website Management

- Surfing
- - Forums
- - Google Research
- - Shop Online
- - Downloads

It sounds like a lot, but I live on computers, and OmniFocus allows me to see the whole lot in one go or split down into any combination.

The logic is fairly simple - it's broken down by specific machine, where a particular machine is needed, or by mindset where it could be done on any machine with suitable software. Actions quite often end up in a parent context (i.e. OSX) if they don't need to be quite so specific.