RIM excels at many things, but keeping secrets ain't one of 'em, so we'd eyeballed the BlackBerry Curve 8900 (nee Javelin) quite a bit before this AT&T-branded one dropped in our laps. It's a Bolder version of the current Curve that improves it in basically every way: Lighter, tighter, but more powerful—and it feels like a phone that was produced in 2008, not when you were still keeping your 2006 resolutions.
Body
It's a solid evolution of the Curve form factor. Slightly thinner, it's also tighter, with less wasted space around the screen and keys. The lines are much cleaner, making it sleeker and more modern, like a sports car compared to a Toyota Corolla. (It's very similar to the Storm.) The refined form has some function, too, since it feels better in your hand. It also has the Storm's dedicated lock key on the roof—no more menu-digging!
Screen
Even though the Curve is RIM's mass market smarty (the Pearl doesn't really count), they didn't scrimp on the screen compared to the Bold. It's fantastic. Colors pop, contrast is great, resolution is solid and the viewing angle is nice and wide. For nitpickers, he colors are noticeably warmer than the Bold—kind of like the iPhone 3G vs. the iPhone—but it's totally fine.
Keyboard and Trackball
The keyboard feels almost exactly the same as the old Curve—punchiness and layout are essentially identical, though the keys now slope ever so slightly, like the Bold, but to a lesser degree. Most people probably won't even notice. The new "atomic trackball" doesn't feel too different compared to the one you're used to, just more robust and less hangin' loose.
Battery Life
We haven't done any formal tests—it'd be unfair since this isn't a final build and the software optimizations can make it even better—but it seems to be comparable to the old Curve (i.e., well over a day), even with the beefier hardware.
OS and Software
Again, this isn't a final unit, so really digging into the OS and software like it's a production model isn't quite fair, but so far, it's a really stable version of the BlackBerry 4.6 OS we've seen on the Bold and Pearl Flip. And obviously, that's where a lot of the improvement is over the old Curve. It's prettier, smoother, and just a better overall user experience, with major enhancements in the look and feel of the entire BlackBerry experience.
The Curve 8900 is fairly nimble getting around the OS, though not quite as zippy as the Bold—but that's expected since the Bold has more monstrous hardware powering it. You can kinda see this in the browser, which lagged behind the Bold in our tests even though both were on Wi-Fi. There will probably be tuneups in the final build to make it snappier, though the Bold will always have a hardware advantage.
Conclusion
What's interesting is that even though the Curve 8900 borrows heavily from the Bold in terms of design and in no way feels cheap (well the plastic-y chrome is a little cheap), it's more clearly differentiated from it than the old Curve was from the 8800. It's very much a Curve still, and clearly the consumer model to the Bold's pro position. So what looked to be a hard choice from leaked shots, isn't quite as difficult as it appeared.
The Bold is more substantial, exuding "executive" to the Curve 8900's "middle manager" or "normal person." It's clearly more powerful, and has a bigger screen. The keyboards are way different, too—personally, I prefer the Bold's larger, squishier keys to the Curve's smaller, stiffer ones. But obviously, the biggest thing is 3G. The Bold has it, the Curve 8900 doesn't, and we missed it sorely.
All that said, this thing will sell like a mother, and justifiably so. It pushes the BlackBerry you see in most people's hands (if they're carrying a BlackBerry) into 2008, exceeding the original Curve in every way.