In short, you can go to your place page in Google, click on impressions, and then at the top right of the page, it gives you a box to post something to your place page. If you try it, it might appear to work, but your place page won't show the post.
Google's Ashley said this is a known issue:
This is actually a known issue and we are working towards a solution. Hopefully it will be back up and running soon!
There is not ETA for a fix but I am honestly not sure how often this feature is used.
Forum discussion at Google Places Help.