Well I bought the Kobo Glo and it arrived on Saturday - today, Monday I returned it!
I was in two minds whether to keep it or not as I really like so much about it - tap to page turn, no buttons (so smaller size), plenty of fonts and easy to add more, widely adjustable font sizes, adjustable line spacing and probably more I can't remember right now. Side loading books was easy and setting up Shelves (Collections) using Calibre was easy. Some of my side loaded reformatted ePubs were showing with no side margin but I understand that is an easy automated Calibre fix too - I just didn't get around to doing it.
Why did I return it? Firstly, I bought it to read in a dimly lit room without a separate clip on light. For me, the light was too bright even on the lowest setting. It also made my eyes ache, they felt tired and gritty just like when using a backlit screen. The light itself was fairly even, no coloured spots or bright/dark pixels, but on a very low setting it was slightly brighter around the sides of the page, nothing really bad though. The speed of operation of the 1GHz processor was good, as was the responsiveness of the touch screen. Maybe slightly faster and more responsive than the 650, but not obviously so.
Over the two days I used the Glo I read 1.5 books so gave it a good test run for the purpose for which I bought it. (I didn't test wifi or buying books from the device as this is something I never do. I prefer to buy from different places, download to my computer, strip DRM and then side load onto the reader.) I found myself reading with the light off most of the time and when I compared the screen with my 650, I couldn't see any noticeable difference with regard to whiteness of the screen. It did freeze twice during the two days, but I was playing around alot (like going from smallest size to largest) font size, line spacing and different fonts at the same time - while I was reading and generally moving between screens, it behaved perfectly. My opinion is that the Sony rarely freezes because there isn't much you can do to change things, keeping it simple and playing it safe makes for a stable user experience. Personally, I would rather have the option to tweak the fonts and lines to suit myself and risk the occasional crash. Of course there was an obvious difference in overall quality of the device when holding it - after all the 650 new cost twice as much as the Glo - but I would be prepared to give up the (cold in winter) metal casing for a lighter and smaller device.
However, overall, I couldn't justify paying the £99 just for the option of tweaking a few settings, although I was very tempted. My wish list for my next reader is as small and light as possible while keeping a 6" screen, higher resolution, plenty of fonts, font sizes and line spacing options, fast processor speeds, not black plastic, low price, open to all stores/file types. I suppose if I could source different parts from existing readers, I could come up with a device I would find worthwhile upgrading to, but none of the currently available devices fit my requirements. My next move? To get access to a PC so I can install PRS+ on my faithful 650.