1.3 GHz is not bad at all for an ARM. It's not trying to compete with x86 for the performance crown. It's decently fast and runs linux apps like a web browser just fine.
Novena's 64 bit memory interface might actually make a big difference. From my tests, a 1080p 32 bit framebuffer uses up around 1/4 of the system memory bandwidth with a 32 bit DDR3 interface.
I also get the feeling that desktop browsers (chromium, firefox) aren't very well optimised for ARM.
Freescale provides hardware video decoding support for Chromium's GPU media stack[1].
chrome://gpu snippet on my Sabre Lite running Chromium 37.0.2062.120:
Graphics Feature Status
* Canvas: Software only. Hardware acceleration disabled
* Flash: Hardware accelerated
* Flash Stage3D: Hardware accelerated
* Flash Stage3D Baseline profile: Hardware accelerated
* Compositing: Hardware accelerated and threaded
* Rasterization: Hardware accelerated
* Threaded Rasterization: Enabled
* Video Decode: Hardware accelerated
* Video Encode: Hardware accelerated
* WebGL: Hardware accelerated
I'm mostly working on software for ARM and since all the tools I need for work run well enough, why not? I still use x86 at home.
> which ARM machines have you been using as desktop replacements?
The ones I've used most were IMX53QSB, then ODROID-X2, ODROID-XU and I'm now switching to ODROID-XU3.
> What advantages do they have over x86 machines?
I was able to get rid of the x86 desktop while only using ARM hardware I would have used anyway. Also, the boards have a tiny footprint (you can tape several to the back of a monitor for example), they're very low power and can be passively cooled. They're very cheap too.
I've also used some RK3188-based mini PCs dongles for their portability. You can carry a reasonably fast GNU/Linux machine in your pocket and don't cost much more than Raspberry Pi, which I find way too slow.
I know the variety of hardware; started with ZX Spectrum (3.5 MHz 8-bit Z80), programmed TCP stack on a 25 MHz 16-bit CPU and I could be fine with a six-year-old laptop (typing on one, actually). Still, premium-priced laptop could use more power; especially if it's ARM, there's never too much.