I have noticed this as well, when I was preparing PB360+ devices for several people around me.
I have copied my favourite fonts over, and I couldn't find configuration where the fonts would look good. Unfortunately the Christmas were drawing close and I had to hand over the gadgets ;-)
I had concluded that the new owners would have to find fonts that look good on the new readers.
I think it is caused by different software for rendering text, or perhaps just different setting in the antialiasing.
This is one of reasons I am in no hurry to switch from my PB360 to PB360+.
Another reason is that I found the browser in the newest PB360+ firmware completely useless. Perhaps developers were too preoccupied testing it on touch-enabled devices - I have heard that PB602 devices are not in production anymore.