Google has enabled Google Apps users to begin using Google+. This should increase the number of Google+ users, and make it easier for Apps users to participate in Google +. Check out the official blog post noted above and review the requirements and precautions within your organization's Google Apps account (Google+ requires Picasa Web Albums and Google Talk to be enabled for the organization).
Be aware that Google+ profiles fall under the control of the business or organization. One change for Google Apps users is that you will have the option to share with everyone in your organization, even if you haven't added all of those people to a circle.
For people who started using Google+ with a personal Google account, and would prefer to use a Google Apps account, there will be a migration tool released in the near future (reportedly in a few weeks). Hopefully, the migration tool will work in the opposite way as well. If one leaves an organization, it would ideal to move your Google+ profile to your personal account.