iOS 8.1 brings bug fixes, speed improvements, and interface changes, but it also enables Continuity features such as Text Message Forwarding and Instant Hotspot, allowing iOS devices to better integrate with each other and Macs running OS X Yosemite. With iOS 8.1, Apple is opening access to its iCloud Photo Library beta – an iCloud service that stores all your photos from all your devices, in a single library that relays changes to every device. And last, iOS 8.1 marks the debut of Apple Pay, the company's new payment service that rolls out in the US today.
If you kinda loose track of what new features is bringing iOS 8.1, this MacStories article from Federico Vittci is, as usual, great.
For me, I'm pretty exited for the "Text Message Forwarding feature", which will bring the ability to respond to my SMS friends (the majority) directly from my iPad, and, someday, my hypothetical Mac.
I just activated the iPhoto Cloud Library to see the improvements (and it's uploading a lot of files), but this is not a feature that I'm particularly exited for, since I already back up my photos with Carousel (from Dropbox) and OneDrive (thanks to my 1 To storage space from my Office 365 subscription), so not a big deal from now. But we'll see the Apple implementation.
Also, the big feature that I'm waiting for is Apple Pay, but unfortunately, it's not available in Europe, and, anyways, since I have an iPhone 5, I'm not eligible to it. I'd like to see if it's worth the upgrade to an iPhone 6.
Anyways, I hope you'll enjoy the update!
Edit : Oh, and if you're looking for an extensive changelog of the update, Jason Snell of Six Colors got you covered.