I use the Sony T1 (Rooted, Kindled, with Coolreader as my primary app) for reading at home. When I go out and expect to wait for a while, I slip the PB360 into a pocket.
The Kindle Touch I gave to my mother to replace her fading (literally) K2.
I haven't touched the PB701 since I got the Sony; I don't miss the color or the weight.
Generally I get a new reader when I see a compelling feature at a reasonable price. Which isn't often; every other year or so. Right now I doubt I'll be too interested in the T2 or K6. But if something catches my eye, I can always flip the T1 to a relative...