Actually, Mountain Lion expands on two different kinds of sharing:
- Sharing your content with yourself among multiple Macs and iOS devices (iPhone, iPad)
- Sharing your content with your friends and the rest of the world.
What if you only have one Mac and no iOS devices? Read this tip for more info.
Also, check out the iCloud series I wrote last summer for more info on iCloud.
Besides sharing your content between devices, you can also easily share your content with the world. The Share icon (see image above) is in practically every app. Clicking the share button brings up a list of ways to Share: Email, Messages, AirDrop and Twitter. Images can be shared with Flickr. It's not available now, but starting this Fall, you will be able to share directly to Facebook as well.
(more on Messages and AirDrop in future tips)
Here is what Mountain Lion is NOT:
A few folks out there are claiming that Apple is forcing you to share, and by extension making you give Apple all of your logins to all of the services you use. Not true at all.
I don't tweet. I don't read tweets. I don't care what my friends eat for lunch and I don't need to see a picture of a sandwich from Jimmy John's. Fair enough. I haven't logged into Twitter and I can calmly ignore the Twitter option on the sharing options. In fact, I was never even asked to log in to Twitter when I upgraded to Mountain Lion. You get asked to log in to a service the first time you try to use it.
iCloud is pretty much the same. Yes, you are asked for your Apple ID after the upgrade to Mountain Lion, but if you don't want to enter it, you can just click Skip. An Apple ID is required for purchases in the iTunes Store, the Mac App Store and iCloud. You can live without any of the three if you so desire.
An Apple ID is the "key" that brings all of your devices together for sharing. I find it to be an amazing tool with two Macs, an iPhone and and iPad in the family. But, again, no one is forcing you to use it.