Talk about up-again, down-again. It was just a year ago when a global shortages of 2010 Toyota Prius models kept supplies tight all over the world. Now, they may start to pile up on dealer lots again.

Last summer, the company had just launched the all-new 2010 Prius, the third generation of the industry's iconic hybrid-electric vehicle. And incentive schemes in the U.S. (remember Cash for Clunkers?) and Japan kept them scarce on the ground.

Now, according to Bloomberg, the end of a year-long Japanese new-car incentive scheme that heavily favored the most fuel efficient models means that Prius sales are likely to tumble in its home market.

The 2010 Prius spent more than a year as Japan's best-selling car, largely due to that same incentive scheme.

But the prospect of declining Prius sales with the end of incentives may have contributed to Toyota's recent curtailing of its aggressive hybrid-production goals for 2011.

Following the aftermath of the 2007 gasoline-price spike, moreover, Toyota made aggressive plans to double its capacity to build hybrid vehicles--which had been constrained by supplies of the nickel-metal-hydride battery packs that store recaptured energy and use it to help power the vehicle.

Still, the 2010 Prius remains the distinction of having the highest EPA fuel economy rating of any vehicle sold in the U.S., at a combined 50 miles per gallon. And it remains Toyota's third best-selling passenger car, after the Camry and Corolla.

With additional Prius models in the pipeline, perhaps there'll be another burst of interest in the hybrid.

And it's a dead certainty that when U.S. gasoline prices rise past their current level of $2.70 per gallon or so, the Prius will again appear on new-car buyers' dance cards.

After all, we've seen this movie before.