I have tried using rather many websites which are created for posting sticky notes but recently I realised that my favourite site is linoit.com. Here are two examples how I used it with my students.
here. They have a class blog, so they did not experience any difficulties posting their replies.
The task was elementary - they had to complete a grammar exercise in the classroom and (after showing it to me) immediately go to the media library one by one, enter the website (I had supplied the address) and post the exact time. I stayed in the classroom and watched them posting the stickies. When they returned to the classroom, we discussed the tool and its possible uses.
Needless to say, they were delighted with the activity, especially after they had attached the picture of the naughtiest boy in class. For beginners, their joy was natural, and I had reached my aim - to get them interested in using web tools for making learning more exciting.