I'm no longer involved with CardMeeting, but the project's carrying on without me.
The problem with electronic tools (even CardMeeting) is that they are very limited compared to physical
cards. Physical
cards are tactile and can use a huge display area. They're 300dpi and can be spread out over a 10' table, then hung up with magnets on a whiteboard and rolled back to the team room. The whole team can participate at once. You can physically take the card you're working on and clip it to your monitor. When somebody makes a request, you can whip out a card, have them write it down, and then walk over to the planning board and insert it into the plan... immediately. You can even have electronic backups by taking a digital picture of the whole board. (8 megapixel cameras have enough resolution to capture the whole board in one picture.)
Electronic tools are incredibly clunky in comparison. They're good for just one thing: multi-site teams. In fact, our design goal with CardMeeting was to replicate the experience of multiple people using physical cards around a table.
Unless you have a multi-site team, I recommend sticking with physical cards.