For quite some good reasons, Pentax users, particularly K10D ones, wish to get back to older version of firmware for their DSLRs. A quick search on major Pentax forums will reveal such queries easily.
One of the major "drives" for those users to "downgrade" is that they encountered focusing problem so that they need to get back to the earlier version 1.10, which has the engineering service mode access method disclosed and in that mode there is a parameter that can be input to compensate for the AF error and as such the Front Focusing (FF) or Back Focusing (BF) problems can be cured partially, at least for particular lens and under specific lighting condition, say, tungsten environment.
Now that some people have found that SDM focusing could produce more AF errors, i.e., BF or FF. So, I and some people have thought about why not try an older firmware and see if there is a difference and if the problem can be cured?
Now, the problem is how to downgrade the firmware, which is not allowed by design. As when the user tries to re-program a "new" copy of firmware to the camera, there must be a version checking process which will only allow upgrade, or at least re-programming of the same version, but not an downgrade. Pentax have assumed that users should and will never look back. But of course, this is not the case in real life.
So, here comes a method for downgrading from version 1.11 to 1.10. In fact, the working principle is simply to cheat the existing firmware for the "new" firmware version. Just change the old firmware file's header, using any Hex Editor (click here for a list of free Hex Editors), to replace the string(s) of actual firmware version to the latest version number, say, it can be even 1.30. It is said that one can then program/write over the existing firmware. And then, if one still want to have complete original old firmware to be installed in his camera, the author said that now the original old firmware, without any modification, can now be then downloaded back to the camera by just using the usual procedures for firmware "upgrade". Well, a copy of the original untouched K10D firmware version 1.10 can be found here.
Good luck and happy downgrading (and actually hacking)! ;-) But do remember try everything at your own risk and you should be the one who knows what you are doing, and why you need to do so, the risk involved and the possible consequence(s) thereafter!
Update (Nov. 25): All the K10D firmware versions can be found here, officially:-
http://www.pentax.ca/digital/digital_slr/k10d/firmware_110.php
http://www.pentax.ca/digital/digital_slr/k10d/firmware_111.php
http://www.pentax.ca/digital/digital_slr/k10d/firmware_120.php
http://www.pentax.ca/digital/digital_slr/k10d/firmware_130.php
How long Pentax Canada will keep the older versions is yet a question, though, as it seems that it's Pentax's central policy to remove older version of the firmware for downloading once a newer one is available.
Update (Dec. 16): For those who do not want to do the Hex editing, an already modified copy of the firmware version 1.10, which can be used to write over the latest firmware version 1.30, can be downloaded at the page below:-
http://www.vietzon.com/red/forums/viewtopic.php?f=7&t=33
If you still feel unsafe or uncomfortable or whatsoever with this "hacked" version, just write over it with the original 1.10 that can be obtained in the Pentax Canada link mentioned above and then the downgrade will be perfectly completed.