Well, here's my $.02
I bought both the Kindle and the Sony 505 about a month ago to test them concurrently and then decide which to keep. If you're interested in the specifics of my experience, you can search my old threads and see my pros and cons.
Suffice to say, I bought the Sony after giving them both a workout. I had some issues when I first decided to keep the Sony--several hours, in fact, of sweating and swearing while trying to figure out the conversion to .lrf from .lit using ConvertLit and Calibre was the most major hurdle. Now that I've got that totally under control, I've been able to enjoy the 505 immensely.
And, since I bought the Sony, I've noticed some major changes in my reading habits as a result, such as:
1) I'm reading a LOT more. The small size and easy portability of the Sony make it much more likely that I'll carry it with me and read everywhere
2) I'm discovering a lot of new authors (like Cory Doctorow, for example. I probably would never heard of him were it not for this board, and my Sony).
3) I don't worry anymore about ruining a book by reading in the bathtub. I put the Sony in a quart size freezer Ziploc, get in the tub, and it's like Calgon, take me away!
(TMI, I know)
4) My house isn't being overrun by books. I love pbooks, but I've downloaded 50 books for the Sony since I've had it, and I don't even know where I'd put all those books if they were pbooks. So I'm willing to spend more on books knowing I'm not going to have to buy another bookcase along with them.
So in short, I love my Sony. While it would be a bit of an overstatement to say it's revolutionized my reading experience, it has certainly enhanced and revitalized it!