Do you monitor the student's laptop screens with an application like Altiris Vision to prevent students from using tools that are not allowed on the test? What prevented a student from finding a complete English translation of In Taberna on the web and then uploading bits of "translated" text to the twitter feed and ultimately the blog without ever doing any real translating at all?
Low-tech answer: I have students clear the browser cache before starting an exam. Then they open only the 'allowed' sites as tabs in a single browser. I can either do random spot checks where I look at the browser history / recently closed tabs or when the students submit their tests, I could have them submit a screen shot of their browser histories showing the time the test was turned in.
Either method just takes a moment of time.
In terms of pre-loading things to Twitter: I'm following the feed myself and have access to all of their sends. I also do random DM checks to make sure they haven't used that feature to crib notes.
All that said, I really haven't had a problem.
Early in the year I caught a bunch of kids doing something inappropriate online regarding something they had actually put on their blogs. And so, before class one day, I projected the offensive item up on the wall and left the room. By the time I got back a few minutes later, all of the students had come in and were sitting at their desks silently. I pulled the projection and started class.
Never said a word about it again, and haven't had to deal with inappropriate messages on blogs again.
I'm generally against the use of spying software. I tried out SynchronEyes, but quickly found a simple hack around it. Seems like you could throw all the money you wanted to into any of that sort of software and someone will find a hole. Even more importantly, however, I think that sort of software sends the wrong message. I don't want my students to think of me as Big Brother. My classroom is built on trust. Where's the trust in that?
There are plenty of human options for cutting down on cheating. It's really all a matter of how you run your class.
The kids think they know whether they can pull one over on you or not. So in my class, I demonstrate to them all of the ways to pull one over on me. And then I demonstrate to them exactly how I catch those things.
I guess it's a matter of transparency.