I've been having a recurring dream lately. No, not the one where Betty White teaches me to hot-wire a car. Instead I'm in the future, using some sort of "post-PC" device that combines the best of my laptop and tablet. It's the perfect hybrid of convenience and efficiency.

Then last week, Microsoft introduced the Surface Pro 3. It looked as if the dream had come true.

In fact, at its news conference, the head of the Surface team directly said that this device would meet my expectations of the laptop of the future. Sometimes real life can be stranger than dreams.

Yes, Microsoft is confident that—with a larger, higher-resolution 12-inch HD screen, new keyboard, improved kickstand and $799 starting price—its new Surface Pro 3 tablet can replace not my iPad, but my beloved 13-inch MacBook Air.

So I tested that claim. For the last week, my laptop has lived under my bed as I've spent my waking life with the Pro 3. On its third attempt, Microsoft has leapt forward in bringing the tablet and laptop together—and bringing the laptop into the future. But the Pro 3 also suffers from the Surface curse: You still make considerable compromises for getting everything in one package.