I read about WallWisher a couple of months ago on Free Tech for Teachers. WallWisher allows you to set up a quick "wall," to which users can add "sticky notes." No sign-in needed, and the creator can moderate before allowing a note to appear.
I hadn't figured out a good way to incorporate it into a lesson yet. I was overthinking! It's perfect for a quick review. Yesterday, I was introducing a lesson on Australia, and I needed to review some background reading that they had done for homework. I set up a Facts about Australia WallWisher, and had student groups of 4 work on adding facts they remembered from the reading using laptops. I set a timer, so there was a great sense of urgency as each group tried to get a fact onto the wall before someone else did (I had a "no repeat" requirement).
When the time was up, we did a "List-Group-Label," one of my favorite standby activities for intros and reviews. The listing of facts done already, we moved around the "stickies" on the wall into groups with similar ideas, and gave each category a label. List-Group-Label generally works well with post-its and small groups, but is tougher with the whole class-- lots of little, hard-to-read pieces of paper all over the place. This worked great and provides a record that students can look back at later as a refresher.
With just over 2 weeks left of school, I am planning to use WallWisher for a "This class is about..." wall that this year's students will leave for next year's.