I just bought a "new" (to me) 505. I had a 505, and had a mishap with the screen. I knew, without a doubt, that I wanted another 505. Didn't even consider any other reader, except for the 300, and that was very brief.
I don't plan on buying another anytime soon. I mean, I can only read one ebook at a time. So I would have no use for another ebook reader.
ALTHOUGH......as I was typing this, I realized I DO have the Kindle App on my ipod touch, which enables me to take advantage of free Kindle books. But thats it. I have bought 3 kindle books. So, I'll say I have 1 1/2 ebook readers lol.