I hope they release the 300 at a sub $200 price point - it will certainly get the market going. 440 MB should be more than enough for an entry-lever reader. Although I have my whole library on a 4GB card, I tend to put the books I'm actively interested in on my internal memory and keep the card out to reduce processing and formatting time.
I'll take a look at the 600 when it's available, but I have to say I wasn't too thrilled with the touch screen on the 700. Even discounting the poor contrast - mainly as a result of the light wedge - I found the touch screen didn't work very well for me. I must have low capacitance or something. The page change buttons were OK for my usually left handed hold, but the screen wipe to change was useless one handed. I prefer the 505's left side page turn button.
Of course, what I really liked was the REB1150/1100 big ergonomic page turn buttons.