If I recall correctly, I got used to the flash-to-black in about 20~30 minutes. I haven't really noticed it (except when someone asks about it) in over a year.
If you think of it in comparison to what you see when you turn a physical page, the idea is less disturbing.
All that being said, there are apparently a very small minority of people who find it simply intolerable. I think that in the ... 16 months that Sony devices have been out we've encountered one person here who actually used one for a while whom it just drove to distraction and he couldn't get used to it.
That's a
very small minority though, there's no real reason to believe that you'd be number 2.
If you're particularly concerned about it, I'd suggest you try to find someone near you who has one of these devices and see it for yourself. This forum can actually be good for linking up with other folks near you. A post along the lines of "Hey, I'm in such and such a city, on the Southwest side, and I'd like to see an e-ink reading device -- anyone who's near me and would be willing to let me buy them (and their reading device) a cup of coffee, send me a PM" should do the trick. That's how I say an iLiad when they were first out in June of '06.
I ran into OliverBogler today, actually (turned out we work at the same place). For anyone who remembers him, he's doing well, but sold that iLiad on e-bay when he got a Kindle for Christmas.
