From CUNY Academic Commons (I used in my language classroom as a way to practice vocabulary)
Every week I would give two words and students had to make two posting using this particular word on the class twitter site. I also asked students to interact with each other during the academic year by requiring a certain amount of postings. I made this count as part of their participation grade.

Advantages: it allows a good way for students to interact with each other, and to learn new words in context.

Disadvantages: sometimes the students were limited by the word count. (I used it to create tutorials and video podcasts for teaching languages)

Advantages: I made several videos with this program and it is one of the best software in the market for creating video podcast and tutorials. I made some vidoes to help students learn about Italian culture, grammar and vocabulary. I also used the test feature which is quite cool, the students can mail you the answers to the test once they are done with it.

Disadvantages: It is rather complicated and difficult to learn. It it also very time consuming, and very expensive !!