For these requirements, the Fujitsu Stylistic Q550 has emerged for me and when I found an offer for a used unit on eBay for 270 EUR, I slammed.
The only drawback is the somewhat slow Atom processor for multitasking or computationally intensive audio / image editing. But I knew by internet research beforehand and taken into account for all the other benefits.
A notebook / netbook was eliminated because the dimensions, the weight and the duration (or the prices of higher-value device).
Android Tablets dropped out because Windows request.
I have the 1.5 GHz, 30GB SSD version without UMTS (no GPS) and am just looking for the maximum usable SD card size, which seems to be at 32 GB.
Now, after almost half a week all the important updates software are partly filled, installed and the system optimized for performance by TuneUp Utilities 2013 (Demo Version).
It can be great to work with (see tips on the Internet icon resizing for touch input) and used mini Bluetooth keyboard on eBay is already on its way to me.
An external combo burner has passed the functional test on Q550 today. Soon the external 2GB drive is tuned and tested several devices (HD, burner, digital camera, USB flash drive) to the USB port unfortunately only a hub Spannungsvesorgung.
All in all I am very pleased with this unit and can recommend it for people who have similar needs very.
Addendum 04.02.2013:
Meanwhile, still favorable to get the model with 60 GB SSD and with Bluetooth Keyboard Periboard-804 in almost daily use. It even runs Avid Pro Tools 10 as a professional audio software for recording (SDHC Card 64 GB). Record 16 tracks individually and playback of 16 tracks go well with it (without FX or Elastic Audio etc.). To edit and mix a more powerful PC should be used of course.