There are confirmed reports in the Google Places Help forums that the Google Places post to your place page feature does not work.

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:

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.