I've seen this problem come and go every few Catalyst releases where the CL_DEVICE_MAX_CLOCK_FREQUENCY is reported as 0 (you can see it from clinfo). It seems to come and go; right now I've noticed that on Linux it happens if I'm SSHed in, but not if I'm actually using the display.
There currently is no console support for Linux. I believe that there needs to be an X Server running for OpenCL to work correctly. If X is already running and you still get bad results, try redirecting your display to your host machine.
(I am not a Linux expert.)
Right now it is happening on one system running Ubuntu 11.10 x86_64 with Catalyst 12.1 on a Radeon 4870, and on another Ubuntu system for both a Radeon 5870 and 7970 using the special 7900 driver from http://support.amd.com/us/kbarticles/Pages/catalyst121linuxdriver.aspx
Max clock frequency: 0Mhz
Name: ATI RV770
Vendor: Advanced Micro Devices, Inc.
Device OpenCL C version: OpenCL C 1.0
Driver version: CAL 1.4.1664