So, how do we get 3 images inline within a single post?
1) Share What's New
From the Share What's New box at the top of your stream Select Add Photos.
This will bring up the option for you to add an image from your hard drive.
With the exception of sharing a full album, and more on that later, at this stage it is not possible to add a single image that has already been uploaded to Google and which is now held in your albums at Picasa (however with the speed of changes in Google+ it can't be long before that option is available though!).
Selecting up to 3 images will place them in the Share box ready for you to complete your post.
Once you have finished typing, Share will complete the post and your images will be placed in-line in the completed post.
2) Share from the box at the top right of the Google+ grey bar.
3) Sharing an album via Picasa Web Albums
In all of these options if you try adding more than 3 images they will default to showing as a single large image with subsequent images as small thumbnails beneath.