This article from a couple years ago (sorry, I can't remember who to thank for this link) argues that Chinese power is at a relative peak right now and that after 2008, US power relative to China will begin to grow as various US weapons go online; and that Taiwan will begin to close the China-Taiwan gap as it acquires new weapons and absorbs them. The authors conclude:
First of all, however, U.S. civilian and military leaders must dismiss the fatally flawed theory that time is on China’s side in the struggle over the strait and recognize that the real danger of a PRC attack is in this decade, when Taiwan is most vulnerable, not in the next. Only then will Washington and Taipei act and plan according to a shorter, realistic time line.
As I've mentioned, the US and Taiwan need a sense of urgency. Even if China has little chance of winning a war against Taiwan and deterring or slowing US and Japanese intervention, if time is not on China's side, China may decide to try even a slim chance of successfully invading if the passage of time will make that chance disappear.
I think that time is on our side but for different reasons. I think that the longer democracy is cultivated on Taiwan the less China can afford to bring that virus into communist China and infect 1.3 billion Chinese with the desire for freedom. Nor will Taiwan endure year after year of invasion threat without going nuclear. This article by Bernier and Gold adds another conventional military reason why time is not on China's side.
And there's that year 2008 popping up again. Huh. Is an invasion prior to the Olympics really so far fetched?