I can imagine this would be invaluable in a 1:1 situation but I have also found it very useful in group work. Students often work in groups of three on work flow lessons and I have used Socrative to have them reflect on the lesson and on their finished product. I have also used Socrative to check for understanding in a small group in which each student has an iPad. You can basically set it up to send the next question when all students have answered the last one. Another effective use of the app would be to poll students.
Other fantastic things about Socrative are that it collates and emails the results and that it is absolutely free, just requiring teacher registration.
Someone mentioned the app to me today and it reminded me that I hadn't used it in a while and how much I enjoyed using it. I will definitely be utilising it again very soon.