I can't imagine Google Glass will be exactly cheap either.

Also, just like Segway has been facing regulatory issues [1], Glass deployment might be hampered by safety and privacy issues, at least initially and in some markets.

Not too far-fetched of a comparison really.

[1] http://en.wikipedia.org/wiki/Segway_PT#Restrictions_on_use

They're also somewhat dangerous, having killed the guy who bought the Segway company, among others. That is not mitigated by the fact that the Segway was marketed as something like better walking, discouraging helmet use (even while claiming in safety manuals that helmets are required).

...and not particularly useful.

And mostly useless. Most active people would prefer walking or cycling to maintain their fitness. Most inactive people don't have the coordination and would rather sit down on a mobility scooter. It was a cool idea with a limited market.

Glass will succeed if people find it useful enough and the dorkiness will become cool. It is really an extension of the smartphone user interface and smartphones are undeniably useful. People currently wear glasses and those ridiculous bluetooth earpieces so it isn't a big stretch.