It's handy and easy for the students to use.
In the Virtual HS we use Elluminate for synchronous, online chats. However a nice free model is found at www.scribblar.com. You might want to check this one out as Elluminate is extremely costly.
It's also fun to let the students tweet. Here's a sample...
These tools are very useful. Students like texting (witness their continual posture in class, head tilted down and both hands under their desks) The response for the poll can be tabulated quickly and there are many different ways the poll can be answered.
Twitter is instant and you could project the twitter feed and students can interact with your lecture on the fly without having to interrupt. The question would be there. Other students could interact on the tweet before you were able to get to it, probably answering the question before you get around to it.