In group situations, always use paper. If you have a pre-existing set of information, you can print these on labels or card, or print on paper and guillotine to a convenient size. Ask participants to write one issue on each note. Give participants some minutes for this activity, but ask them to stop when a large majority of participants have stopped. Get all participants to gather at a vertical surface suitable for Post-It notes.
Windows are appropriate.
Encourage participants to place notes, one at a time, on the surface. As each note is placed, other participants may add similar notes in close proximity. When all notes have been placed and grouped, you can optionally name each group. If there are more than 8 people, gathering around a common area may not be convenient. This is not as satisfactory as having the group work together, since it is difficult to keep everyone focused on the task.