First of all, let's look at the original official product press release:-
http://www.sony.co.jp/SonyInfo/News/Press/200708/07-072/index.html
(in Japanese, Excite English Translation Here)
With a 12-channel output architecture, the IMX021 has a maximum frame throughput rate of 10.39 frames per second at full image resolution in 12 bits. So, the K-r has a maximum frame rate of 6 fps for maximum resolution JPEG (which is converted from 12-bit RAW sensor data down to 8 bits per colour channel of the JPEG format) which has not yet fully utilised the full potential of the sensor indeed. Of course, the bottle-neck for this maximum camera shooting rate is not at the sensor anymore.
Other feature of the sensor is a built-in programmable amplifier up to a maximum gain of 24dB. The rated output voltage (sensitivity) of the sensor (at f/5.6 with yellow light source of green colour signal) is in 500mV (or 0.5V, average figure) and the maximum saturated voltage is 1100mV (or 1.1V, minimum figure). If this is compared to the specs of the ancient 10MP CCD sensor ICX493 used in the K10D/K200D/K-m, it could be noted the improvement is not by that much indeed as whilst the IMX021 has slightly better sensitivity (so that there will be slightly less noise owing to less amplification required), the saturation level per pixel is close and similar. As such, it should say that actually the IMX021 is even more vulnerable to suffer from charge overflow which will result in highlight clipping of the pixels and then in the final image. But of course, the better image processing technologies and techniques of the later could always help, so as to compensate for this deficiency and to produce better results ultimately.
Besides, it is interesting to see that the initial set selling price, back to 2007 when it was first announced, of the IMX021 was in 40,000 Japanese Yens, which roughly equalled to be about US$400 by that time. Indeed, it was surely not cheap for the total cost of an entry-level DSLR body. I still remember that when I bought my K-x almost two years ago, it costed me for something just more than US$600. So, the profit margin by the camera manufacturer was really not that much, even though the price of the sensor could have been dropped and that in volume order that it could be cheaper.
For more details about the sensor, here is the product catalogue in pdf:-
http://www.sony.co.jp/Products/SC-HP/cx_pal/vol74/pdf/imx021.pdf
Unfortunately, the catalogue does not contain more information on the video recording part but only mentions once that the sensor supports it. Otherwise, I shall see if it is possible to record 1080p video like what older Canon APS-C CMOS sensor could actually do!
Related:-
Myth? CCD Has Better IQ Than CMOS? (A K-m Vs K-x Shootout and Riddle)
The Secrets of the K10D (Part 1 of 3) - The Heart: CCD Imager
K-r and K-x are Much Different!
Heart of the Pentax Q - Sony IMX078CQK Imager
Inside the Nikon D7000: The K-5 Sensor is There! ;-)