I think they might become mainstream for race bikes. On the other hand I think I wouldn't trust them yet for a multi-day trip or longer marathon. How long is the battery life in your experience?

As with anything electronic, my bet is that within the next 3-5 years the price will drop significantly. Look at digital SLR cameras. The camera that you can find for a few hundred USD nowadays, used to cost almost the price of a small car ten years ago.