UPDATE: More posts on Content Type Hubs here
MOSS 2007
Say for example you have a Site Collection Web Application1 and you have created a series of content types to use. Now, you create Web Application2 and find the necessity to reuse the content types created in Web Application 1. There is no way you could share or reference those content types created in Web Application1 in Web Application2. The only way possible is to create or write an application which would install those content types. This situation is pretty common in large organizations. This can be even considered for exposing base content types you use across multiple web applications in the farm.
Below is the diagram representing the above chaos:
SharePoint 2010
SharePoint 2010 now introduces a new feature called Content Type Hubs.Content Type Hub is a central location where you can manage and publish your content types – so now web applications can subscribe to this hub and pull down the published content types from the hub. Even receive updates on the published content types!
As you can see, the content type hub is exposed to every web application using the Metadata Service Application. So, as long as the web applications use the same Metadata Service Application, the content types will be pushed to those subscribed web applications.
Configuring The Content Type Hub
This is pretty simple.
1) Create the web application and the root site which you want it to be the Hub
2) In the Managed Metadata Service Application (under Central Administration | Application Settings | Service Applications )properties, you can set the Content Type Hub
3) In the Managed Metadata Service Connection, we explicitly tell to consume content types from the hub
4) Now, we can go to our content type hub site, create content types and you should see Manage content type publishing option
5) And publish the same
6) This will publish the content types
Timer Jobs
In order to receive the published content types immediately, you can go and run two timer jobs immediately:
1) Content Type Hub
2) Content Type Subscriber (of the web application which is going to receive the content types updates)
Published Content Types
After running the timer jobs, the content types should be published. Go to your Site Settings | Site Collection Administration | Content Type Publishing
You can see all the published content types here 
Remember, as long as the Web Application use the same Metadata Service Application the content type hub is using, it can receive the content types from the hub.
Very neat and useful feature from the SharePoint team!
More posts will follow in the future once we start using it in the real world projects. Big thanks to Steve for his blog post on this.
UPDATE: More posts on Content Type Hubs here
Hi,
I have followed all the steps but I am not able to see in my site settings the ‘Content Type Publishing’.
Thomas
u have to activate the content type syndication hub feature in your site collection
Be aware, if you have activated Document ID feature on the consuming site collection, you have to activate the same feature on the hub. Otherwise the publishing of the content type won’t work.
Hi…
Thank you very much for the post. I have a question regarding the content type security. Can I assign permission on content type i created for specific users? I mean, I want, only set of users to access\read this content type.
Is it possible?
Rgds
Hi
As far as I know this is not possible. The only thing you can do is setting a content type in a protected mode.
Hi Chaks,Thanks for Sharing Knowledge.
We have web application on default zone with NTLM and then we have extend this web application to internet zone for public facing.Now i have content query web part which do query on Managed Metadata and its working fine on intranet zone but not public facing site.last night i did Publish content type and worked for last night but its not now….
any advise on this
Ronak
Hello
I am using the content type hub to publish document content types across the farm. It works fine except for one issue: Document templates.
Each document content type has a template file in our document center. When trying to create a document using a published content type on for example mysite, the document template url is interpreted as something like http://mysite/Documents/MyTemplate.dotx, when it should have been http://docs/Documents/MyTemplate.dotx.
The problem is that the document template url is stripped of the web app’s path. Is there any way to avoid that, or is document content type publishing across web apps just not doable?
Thomas
I am having a similar problem as Thomas expect I am using infopath forms. I would assume this should work but…..
Can any content types be published from any site collection or only from the site collection specified as the content type hub?
Nice post. Here is one more post on content type hub and publishing contemt types in sharepoint 2013
http://sureshpydi.blogspot.in/2013/04/sharepoint-201-content-type-publishing.html