The 2 things that Glass will have to overcome:
1)The not-so-fashionable look. I'm sure this'll be corrected in the future.
2) The way people feel about a device that may or may not be recording them at any given moment. Let's not even mention anything about a red light glowing during recording because we know that'll be hacked out. Google Glass will be able to record you without you knowing, period. People will simply have to accept that or the product will fail or get banned in so many places it'll almost be not worth owning at all unless you're a hardcore geek. Then of course someone does some super slick mod where Glass just looks like any ordinary pair of glasses; then mass paranoia breaks out and either people get over it or any glasses are banned. ;)
Mind you this paranoia will be happening despite the fact we've had wearable hidden HiRes cameras smaller'ish than a penny for over a decade already... http://www.brickhousesecurity.com/product/b-w+indoor+high+re...