Where do I go to find a list or collection of all the posts in Google+ that I have ever marked with the +1 button?
The +1 tab on my G+ profile shows only web sites I +1'ed and not the posts that I plussed when reading my stream.
See the full list of posts, not external websites, +1ed in Google+
google-plusgoogle-plus-1
Related Solutions
See this Google help article on how to enable Google+ for your domain.
As a summary, you need to ensure that Google Talk & Picasa Web Albums are enabled before you can switch on Google+. Also, if Other Google Services is not available you may have to migrate your organization to the new account infrastructure.
I would also suggest reading the article in full as there are some considerations to take in to account when enabling Google+
To enable Google+
Log in to your Google Apps administrator control panel.
The URL is https://www.google.com/a/cpanel/primary-domain-name, where primary-domain-name is the domain name you used to sign up for Google Apps.
Click Organization & users.
In the pane on the left, choose the organizational unit for which you want to enable Google+.
You can enable Google+ for only specific users, using organizational units. Learn more
Click Services.
Ensure that the following services are turned on for the organizational unit:
Google Talk, which is listed under Core Google Apps suite. If Google Talk doesn’t appear there, you’ll need to add the service to your organization’s Google Apps account. Learn more
Picasa Web Albums, which is listed under Other Google services. If you don’t see the Other Google Services section, you’ll need to migrate your organization’s Google Apps account to the new accounts infrastructure. Learn more
Under Other Google Services, turn on Google+.
Click Save changes.
It may take some time before Google+ is available to all users and they are able to sign up for the service.
There does not seem to be any available add-on/extension that accomplishes this.
Best Answer
Google+ doesn't stream the posts you have +1ed. So you can't retrieve that list.
To Google, that +1 tab is for everything you have found around web and recommended. Inside Google+, +1 for the posts are just a feature to show the post owner that you like that post. That's all.