I've purchase the app iResponse ($1.99) as well as its desktop administration application (Mac only), also called iResponse. The desktop application is free and can be downloaded here: http://www.itate-solutions.com/edu-solutions/iresponse-classroom-responder-sy...

To use this app, your desktop running the admin software must be on the same WiFi network as your iPod Touches. There are instructions on their website for creating a quick ad-hoc network if one is required.

You fire up the desktop app, and create a session, creating a class ID and naming the session. The class ID is what the iPods use to connect to the session:

You must then click Start Session to begin.

The students then fire up the iResponse app on the iPods, and enter their names, as well as the session name, to connect:

Once connected, the response software looks like this:

The desktop software shows who has connected:

At this point, the teacher then uses the desktop software to push questions, one at a time, to the response units (iPods). (The questions can be created beforehand, and saved to a file.)

You select the question you wish to ask, and click Transmit Question:

Instantly, the question appears on the student iPods:

After voting, a confirmation appears:

As the teacher, you can also have the response units give instant feedback to students, so they will know right away if they got the question right or not.

As students answer, the teacher gets immediate feedback about who has answered, and what their answers were:

Finally, the teacher has the ability to view a lot of analytical data about the class's performance, individual student performance, and statistics about each question. Very cool.

I've not tried this with a large group yet, so can't tell you how it functions in the wild. Next week we should have a chance to do exactly that!