Back at the office Tuesday after a long holiday break. So lots of questions for me, and a busy day. Good to be back.

It was also the day that Google announced a new mobile phone, the Nexus. Early reviews all say it’s fabulous, as good as the iPhone in many ways. It’s got a much better screen, they say, but correspondingly worse battery life.

Not to be outdone, Apple has been leaking details of their next big thing – a tablet of some sort, to be announced late this month. There’s been lots of speculation about that on the blogs, of course. We can’t figure out what earth-shattering feature might differentiate an Apple tablet from previous, ho-hum tablets. Consensus is that it’s got to be different or Steve Jobs wouldn’t do it. Different and useful. More than “surfing the internet on the can” – which the iPhone and MacBook handle quite well, thank you.

If anybody can, I am sure that Steve Jobs and company will figure out what a tablet is good for – or at least how to wow us enough that we’ll want one, too.

But, wow, that it has come to this. Three years ago, the iPhone turned the cell phone handset business upside down. Now that the competition has caught up, Apple is moving on to something completely different – presumably an entirely new product line. They’ll still be printing money with iPhones.

And we have come to expect that the Steve Jobs won’t do something that’s not revolutionary.

Back to that Google phone. The hardware looks fine, an iPhone knock-off almost as minimalist as Apple’s wares. On the Nexus, the iPhone’s one-button-to-rule-them-all gives way to four buttons and a roller-ball nose.

(See Amit’s post on the back button vs home button design philosophies for the benefits of multiple buttons.)

Based on a brief hands-on with a Droid, I have no doubt that it will handle Gmail and Google apps much better than any phone on earth.

Oh but that home screen – it’s ugly as the Nexus’s name. Google’s marketing shows a wallpaper gray boxes that the reviews say ripple to follow your fingertip on the screen. The reviewers say it’s cool, but in still images make the gray cubes look ckunky.

And yet, in three short years the competition has gone from pushbutton phones (remember Motorola’s Razr) to two iPhone-quality choices – one an Android clone that’s better than the iPhone in significant ways.

And it sounds like Apple plans to respond with something completely different.

Tech products are becoming differentiated as much by aesthetics as features. It’s not about making products that secure a market position (though Apple’s app store policies use some of those old-fashioned tricks, too). It’s about fast teams. Teams that can get things done and drive products to market.

The Google and Apple competition is so interesting because of the firms’ different approaches to innovation. Google’s approach is driven by data, drawn from testing of thousands of users, in hundreds of iterations. Apple’s designs seem to come full-born from the head of Steve Jobs.

Exciting times we live in – and a great time to be shopping for a phone.