I bought a SONY reader about 3 months ago and I kind of think it was a waste.
It's a closed system.
The iRex is way more open. You can install software upgrades as they become available.
So I'd suggest you buy irex if you can spare the money, otherwise just wait.
btw 700$ will buy you a low end laptop which is definitely better value for your money.
sorry to discourage you... I was very enthusiastic too... 3 months ago