Enable Google Plus for Google Apps
Finally! Google Apps users (such as myself) can access Google+ with their Apps account. Until now, you had to sign in with a gmail account. This seems to be common for Google, most of their applications are not available to Apps users to start which is always a pain.
If you are not familiar with Google Apps read more here. Essentially it lets you run your own mail server using the Google infrastructure and Gmail interface. Free for personal use.
UPDATE: It looks like you can’t add your Google Apps account if you have already created a G+ account with gmail. So it looks like you need to delete your old G+ account and create a new one with your Google Apps address. This is going to be a problem for anyone with significant content and contacts already set up with Google+. If you know of a way around this, please let me know by posting in the comments below.