I'm also having the same problem. The timezone was successfully set for about a week at PDT. I changed the timezone to KST and it worked fine for about 2 months. When I tried changing the timezone to London time, I began getting GMT. Now, if I try to change the timezone, it keeps reverting to GMT.
The only other changes I've made to the system that I can think of are following this security guide (pdf)
http://packetstormsecurity.nl/mac-osx/050819-securing-mac-os-x-tiger.pdf
If I open the terminal app and type "date" on the command line, it shows the correct time and timezone. All of the GUI applications are displaying the time in GMT though.
I'm kind of new to OS X, but on Linux, I would just delete the /etc/adjtime file. This file doesn't exist on OS X.
I'm guessing that I changed the permission of a file to read-only, so that's why I'm unable to make permanent changes to the timezone. If I knew where the timezone is stored, that would be a place to start.
As far as the Apr 29 post with the solution, I can't find it either. Any help would be appreciated.