I got asked this once too and just couldn't enthuse - I had got to the end of the interview and decided that they weren't a professional enough outfit for me to want to work for. I ended up saying I would need to think about it and weigh things up against other good offers that I had also had. then emailed the agency to say I did not want it, once I got home.
The question that threw me in my interview the other day - all the other questions I had luckily totally prepared answers for - was 'If you got this job, which areas of the job do you perceive you would need training/development in?' I didn't know what to say - it totally took me by surprise! What are they looking for here? I began by saying that I had already developed a very similar project previously, knew the background really well, and then paused to say 'Hmm, let me think.' And then said that whilst I knew a fair amount, it would be good to completely learn all the most recent policy in the area. And that that would be my intention, prior to beginning post. Lame.
Anyway - I don't think I got it. At all.