Overall CableCARDs have been a disapointment, but the FCC isn't letting them give up. One of the reasons more consumer electronics companies like TiVo haven't released stand alone CableCARD devices is because of the lack of multi-stream support. If TiVo wants to allow you to record two shows at once like your Cable Companies DVR lets you do then you need either 2 CableCARDs or multi-stream support. If a TV manufacturer wants to enable Picture-In-Picture it would also need multi-stream support.
That looks like it may change soon as both Scientific Atlantic and now Motorola have had their multi-stream CableCARDs approved by CableLabs. With any luck we should see them "within the next few months".