Flickr is an image and video hosting service. Photos and videos can be accessed without the need to register for an account, but an account must be made to upload content to the site. One way that this could be implemented into the lesson in a classroom would be teachers giving this as an option for use when students are assigned to create a presentation that involves photos or videos. On problem that may occur would be technology not working properly.
Wordle is a visual depiction of the words contained in a piece of text. It is created by manipulating the words of an input text and arranging them into a kind of graphic. I could implement this into the classroom by having students create a wordle for a text as an assignment. A problem that could take place using this tool would be students using inappropriate words.
Pinterest is an online service that allows you to share images through social networking. Students could create a Pinterest account and post pictures of the things we have learned about or created in the classroom. One problem that may occur would be students looking at things on Pinterest that they should not be looking at.