First, it’s lighter. The iPad weighs three times as much the smaller model of the Kindle. When I’m packing a carry-on, every ounce counts since it will be on my shoulder.

Second, it’s likely that the Kindle will easier to read for long stretches. The resolution of the device is 167 ppi, while the iPad is just 132 ppi. The bigger the number, the closer you come to genuine ink on paper.

Beyond that, there’s a secret but brute-simple tool inside a Kindle. The device that has a free data plan and a crude browser capability. You won’t mistake it for a complete Internet experience, but high-text Web sites like Google News or a simple mail browser interface are possible, if not comfortable.

All that said, the extra 25 percent of ppi and the 1-pound drop in carry weight are going to pale in front of a mature iPad for business travel. When I land in San Francisco I’ll want to know which BART stop gets me closest to the Macworld hall at Moscone. I can’t do this with a Kindle 2.Kindle’s functionality on the Web could well enjoy an improvement, now that the iPad is on the horizon. But the book-buying and reading experience on the iPad–and the iPhone, for that matter– will enjoy the benefits of the Amazon Kindle app, which is ready for iPad.

You only get access to the content to feed that Kindle app by owning a Kindle, however. The device won’t do even a small fraction of what the iPad is designed to do. You’d expect that for a tool investment with Apple that will cost at least $380 more, plus the cost of a $15 monthly data plan.

However, as a road warrior’s tool, especially a warrior who already owns an iPhone, Kindle has its place in my carry on bag.