I've been using Player on an iCreate (the research version of the Roomba) and I noticed some strange behavior that happens as a result of having the Command Module plugged in to the robot. Our setup had a laptop directly connected to the robot, bypassing the Command Module. We were able to start player successfully and connect clients as well. However, after a few seconds (generally no more than 10-15, though there were sometimes exceptions) the robot would stop responding. For instance, if using playerjoy, the robot would move forward briefly and then stop responding to input. The activity light on the iCreate's serial cable would also stop blinking, indicating no data was being transferred between the robot and the computer. Player itself would not show any errors (even with -d 9), and would continue to accept clients. However, the robot would remain unresponsive until restarting Player.
We were able to fix this problem by simply removing the Command Module. Even if the module was turned off, we found this problem still occurred. For the record, we were using Player 2.1.2.
I didn't see this issue documented elsewhere, so I wanted to send it out in case it helps anyone in the future.