If you just want to share your presentation with others, you can touch the share button on the main presentation index screen to share a link via iCloud Drive or you can send a copy of the whole file via iMessage or Mail. The latest version adds support for third-party storage apps like Dropbox as well. There are also options here for syncing your presentation to iTunes or to a remote server via WebDAV.
Another useful feature that comes with making the iOS and Mac versions (mostly) the same is that your work is synced across all devices via iCloud and you don't lose your formatting or layout when switching. This means that changes you make to a presentation on your iPad will be reflected in the same document on your Mac, iPhone, or even the Web version of Keynote you can access on any platform with a Web browser. With iOS 8 and Yosemite, you'll also be able to handoff your work between devices, so you can start a presentation on your iPad, then immediately pick up where you left off on your Mac.
Some notes about the Mac version
All of the iWork apps including Pages, Numbers, and Keynote, were rebuilt from the ground up to share the same features across Mac and mobile so you could do the same things on any device, but in that process, the Mac version ended up with fewer features. There are already a ton of complaints on the Web specifically from Mac users and they have a point: ever since Apple updated all the iWork apps in 2013, the Mac version doesn't have as many features as it did in iWork '09.
Though it's of little consolation for Mac users, what is most likely going to happen is Apple will add in new (and old) features over time that make sense on each platform. In an attempt to keep users of the older versions happy, Apple has left iWork '09 alone (not replacing it with the upgrade), so if you miss certain functionality, you can still use the older version. Obviously, it's not an ideal situation for users, but there are going to be some growing pains for the time being after making the apps on both platforms share features and functionality.
So, the bottom line is, if you use Keynote on your Mac, I do not recommend you pay for the app unless you can download it for free on a new Mac. Otherwise, stick with iWork '09 until Apple makes the promised changes to all versions.
New features in the latest version
Since its launch in 2013, Apple has been adding new features (and some old ones) to bring the Mac version closer to what it was in iWork '09 and making the iOS versions stronger. The latest version adds trace animations, new presenter display layouts, and the ability to pair Keynote with nearby iOS devices using Multipeer Connectivity.
All the iWork apps now have support for iCloud Drive and you can now use third-party storage apps like Dropbox. Sharing has improved with handoff features (for sharing with yourself, if you will) and the apps give you more sharing options that let you send through third-party services such as Gmail.
The latest version adds a custom color mixer to the iPad version and you can sample colors in your documents using the color picker and apply them to other parts of your presentation for a unified look.
You also can take photos and videos from within the app; add labels to columns and rows in tables; and new inter-table alignment guides make the objects and words in each field look more precise.
So, while the Mac version continues to lag behind iWork '09, it's improving with every update. But iOS versions keep improving over the last version, making work while on the go better than ever.
How does it compare with Google Docs?
Now that the iWork apps are free, there's going to be comparisons with the Google Docs set of productivity tools. They both have spreadsheet, presentation, and word processing tools, and sync across devices using their own cloud services (iCloud and Google Drive). But it's important to note that the new iWork apps are only free for people who buy new Apple devices, or those who have already bought the earlier versions of the apps. In other words, people who don't have a new device or the previous versions of the iWork apps will still have to pay. The new versions are useful on iOS and I still recommend you get them, even with the steep $9.99 price tag. It's worth it for the templates, the touch-friendly interface, and the Apple ecosystem that works seamlessly across apps and devices.
With regard to Keynote specifically, there is no replacement from Google Docs on iOS devices to make presentations. In fact, the new iOS version offers more themes, more and smarter transitions, and a more elegant interface design than what you see on the Google Docs presentation tools even on the desktop. In other words, for building presentations on either desktop or mobile, Keynote beats Google Docs pretty handily.
Keynote for iOS is a step up from the old version, with new themes, animations, and transitions, not to mention a redesigned interface that offers a better layout than what we had before. Putting the iOS and Mac versions on a level playing field means that your presentations are always synced to every device, and your presentations will work well regardless of which platform you're viewing them on.
Unfortunately, Mac users will not be as pleased with the new version because much of the functionality found in the old desktop version is no longer there. Like I mentioned earlier, Apple is bringing many of the most popular features back over time, but also let people keep iWork '09 for the time being to keep that functionality (in other words, this update doesn't replace your old installation). In other words, for now, only get Keynote for Mac if you can get it for free with a new desktop or laptop and wait for Apple to add to the current version before switching over.
Still, if you primarily use Keynote on your iOS device, the new version continues to improve with every update. Though it's not free for all like Google Docs, it offers more tools for presentations across all your devices. Eventually, when we all move on to new iOS devices, Keynote will be free for everyone, but in the meantime, it's worth it to pay for this update on iOS for a marked improvement over the last version.