Except technically I turned it into an Android tablet. I rooted it and overwrote the firmware with CyanogenMod v 11-20140403-NIGHTLY-encore
Of course that's very heavily out of date now. But it does what I want it to do - that is, read books. I just get lots of epubs and feed them to Moon Reader and read away.
Boy it's slow though with an Armv7 CPU with 500MB of memory. But who needs fast when all I use it for is reading one static page of text at a time?
Frankly, I'm astounded it has lasted this long - I'm especially surprised at the battery not having given up the ghost yet. I can get enough reading time to last say 4 or 5 hours in one go, but usually get drowsy enough to get to sleep well before that.
I'm waiting for the battery to finally give in - then begins the search for a replacement battery. In fact, the battery has outlasted the Nook Color charging cable, which frayed at the interface between the cable and one end. So I use a normal USB cable to charge it - which means slow charging.
A while back I looked into perhaps trying to update the version of Android on it - but by now most if not all of the Nook Color hacking sites have gone the way of the Dodo :)