I had my new 650 for about 2 weeks now so I have noticed some good things and some slightly annoying things about it compared to my trusty 505.
Good
Screen is excellent and doesn't fade in direct sunlight. My 505 partly faded when direct sunlight after awhile. Screen is much whiter and heaps faster page turns when I read the same ebook on both devices.
Database refreshes heaps faster when you unplug it from computer than what the 505 does.
Dictionary lookup is excellent. I don't know how we did without it before. I used to just skip over words I didn't know before as I couldn't be bothered finding out the definition.
Slightly annoying.
DC charge jack is now gone so you can't read while charging

USB cable is now micro instead of mini meaning my usb charger can no longer be used until I buy a spare cable to plug into my charger.
Sometimes the page doesn't turn when you swipe and a couple of times it didn't turn when I clicked the button. Anyone else had that happen ?
I think there's a problem with creating collections on the reader.The added order doesn't seem to match the order you added them on. If you add them in a bulk lot it seems to pick it own order when you look at the collection. If you pick them one by one the order seems to change when you check it later. Quite strange I'll have to see if this happens when you create collections with the Sony Library software instead.