In general, the user should be using a microphone as close to his/her mouth as possible. This reduces noise coming from their environment. If the user is sitting in a quiet room they can afford to have the microphone sitting several feet away from them, but if they're working in a cubicle they must wear a headset microphone that positions the microphone only a few centimeters away from their mouth.
For a cubicle office worker to user speech recognition he/she must wear a headset microphone. Unfortunately, many people don't like to be tethered so this limits the utility of speech recognition for applications targeted at users in cubicles.