I am in the middle of downloading the update right now. It's taking forever via my wireless modem. 22 minutes to go and counting.
According to user reports on The Unofficial Apple Weblog, there are no new features found on iPhones updated to the new firmware, and no one has been able to locate the SDK from Apple.
It looks like today might have been the original day planned for the SDK to go live, but as we know, it has been delayed a bit. Stay tuned for more info once the firmware update is complete.
Update -- 2:25 PM
After waiting about 20 minutes for the update to download, I began the update process. It took about 10 minutes from start to finish for the iPhone to update the firmware, reboot, and reactivate itself on the network. I didn't have any problems, though some users have reported random errors during the update process.
I have checked every last screen on the phone, and from what I can tell (which is in line with other user reports) there are no new features included with this update. According to the Apple text file, the update only provided "bug fixes." Which bugs it fixed, Apple did not clarify. Some users, however, are reporting improvements with the way multiple Web pages will load in the Safari browser.
TUAW's Erica Sadun took a close look under the hood at the new build's frameworks, and reports that there are no new ones and it appears that nothing was added.
Most people suspect--as do I--that the update lays the groundwork for the iPhone to support SDK-developed apps. Of course, the SDK is still not available, so this won't be confirmed until it is.
One thing of note to all you iPhone jailbreakers out there. The ZiPhone jailbreaking software does indeed work. That means you don't have to wait for a new hack to unlock 1.1.4, the same unlocking tool you used for 1.1.3 will open up 1.1.4.