Unfortunately, Apple wouldn't let me actually interact with the Watch's UI, as the demo units were simply rolling through screenshots while it was strapped to my wrist. I got to try on both the regular polished steel model with a leather loop strap and one of the aluminum Sport versions. As you'd expect, the build quality of each model was impeccable, with a smooth-scrolling crown control and a satisfyingly solid "snick" happening when pressing it or the button situated alongside. Whether gold, steel or aluminum, it's clear that every Watch has been designed and crafted with care -- and manufactured to Apple's usual lofty standards. That said, it's still a fairly bulky thing to have on your wrist (in both sizes), and no matter how many bands Apple makes for it, we're not sure that the Watch's looks will appeal to everyone. It's not always hip to be a square in the smartwatch game, after all.
The bands were both comfy, though I preferred the look and feel of the leather loop. The magnets inside the leather seem to do the job of clasping well, though perhaps without the same magnetic force as those on the MagSafe connectors found on Apple laptops. As for the rubber sport band, I had some trouble fitting the metal nubbin into its appropriate hole, and I got a little pinch on the underside of my wrist when tucking it into the band. I imagine I'd get the hang of fitting it quickly and painlessly eventually, but my first time strapping it on was not all pleasant.
Update: We had a few questions about the Apple Watch after the keynote, so we asked company reps for some additional details. First, the Watch isn't waterproof -- just water-resistant. Exact ratings are still unknown, but these watches clearly aren't something you want to be wearing when pushed into a pool or jumping into the ocean; they should withstand splashing, snow and other minimal exposure to this particular element, but since the mic and speakers aren't protected, do so at your own risk.
Additionally, while the Watch can monitor many activities, sleeping apparently isn't on the agenda (unless an enterprising developer finds a way to make it work, perhaps). We also pushed for more details on battery life, but the company remains tight-lipped for now. Apple's usually quick to brag about such details in its keynotes when they're available, so its lack of coverage is likely due to the fact that it still needs some more work before the final models hit the shelves. They also showed off the inductive charger, which appears to be very similar to the company's MagSafe chargers (though they insisted they're not the same); when I asked reps if it could get charged on wireless charging pads like Qi or Rezence, they only replied by saying that there are more details that will be announced closer to launch.
We also confirmed that the Apple Watch indeed features an ambient light sensor, so it'll be able to adjust brightness to match whatever lighting conditions it's in.
Jonathan Hall, Zach Honig and Brad Molen contributed to this post.