I have a PRS-505, that I've had for years, and it has served me well. My only complaint with it has been poor PDF performance (some PDFs take 10-20 seconds for a page turn). Given that I don't use a lot of PDFs, and mostly use it for fiction ePubs, I am fine with it.
However, after seeing the glowlight, I am seriously considering getting a new one. I've toyed with the idea for a while of getting a rootable Android based tablet, so I can do some different tasks, but that's mainly been just a whim. Not really actively thought of replacing my 505, until I saw the glowlight. Now, I've still not ruled out nonlit devices, but that's mostly been a way of me having a way to talk myself out of getting a new reader. Reason for it, is I am frequently in situations where lighting isn't always the best. In those times, I now whip out my phone and screw around on that. It'd be nice if I could read as well.