Early on we had some people who did not think they would like visual management. They did not like the idea of putting every work item on a card. It seemed a waste of effort to them. They wanted to sub-optimize for their personal ease rather than for the team collaboration.
The virtual Kanban board we were using at the time offered the ability to add lists to each card. So one person made a few cards with large lists on them. They felt they had saved time. This particular supplier’s UI hid the list on the card.
So when the team met at the board each morning, the work was not visible to the entire team. This person had sub optimized for their own cycle time rather than for the entire team. The team could not easily see the bottle necks because there were not visual cues for each work item that this person had put inside a single card. That card did not move to different process step columns for a long time. This "savings" he had tried actually stopped the team from seeing what was happening with his work.
Therefore we suggest avoiding the urge to batch many items in a list on a single card. This is technically using Kanban, but it is not applying Lean principles for smaller batch sizes. It also does not make the work visible as well as the team needs to collaborate easily.
During Retrospectives, the team realized they needed to see the work better. Then they switched to using one Kanban card for one work item. This may have taken a little bit longer to set up initially, but it helped the team the entire duration of the project to better see the progress and the bottlenecks and how to remove any impediments more quickly.
Since then we have noticed another supplier, Trello, shows the list on the card front, which allows the team to see it.
Whether you decide to put one task per card or allow lists on cards, check out Trello.com. Their product can be organized like a Kanban board easily.