Verdy - I bought a headset from a company called Tamms direct on the internet, it was about £40 as I didn;t want to take any chances with the recognition being inaccurate, however a colleague of mine just uses the standard one and doesn't have any problems using it.
Rick - I use for interviews, it obviously only recognises my voice, but I just listen to the tape through the headset and repeat what the interviewee says back into the microphone, each time I lead it with the persons name, so I know who said what - not sure how this would work for your focus groups, depends how large a group I guess.