I have a very similar problem with my core i5 520 M (2 cores, 4 threads).
But, not as the previous case, my CPU never scales up. In fact I never manage to make it scale, it is always blocked to the lowest frequency.

For me, it may be a kernel problem. With the stock kernel provide by Maverick 10.10 Final :
Linux BlackBeast-T410 2.6.35-22-generic #33-Ubuntu SMP Sun Sep 19 20:32:27 UTC 2010 x86_64 GNU/Linux

cpufreq-info shows me for all virtual cores :

analyzing CPU 3:
  driver: acpi-cpufreq
  CPUs which run at the same hardware frequency: 0 1 2 3
  CPUs which need to have their frequency coordinated by software: 3
  maximum transition latency: 10.0 us.
  hardware limits: 1.20 GHz - 2.40 GHz
  available frequency steps: 2.40 GHz, 2.40 GHz, 2.27 GHz, 2.13 GHz, 2.00 GHz, 1.87 GHz, 1.73 GHz, 1.60 GHz, 1.47 GHz, 1.33 GHz, 1.20 GHz
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance
  current policy: frequency should be within 1.20 GHz and 1.20 GHz.
                  The governor "ondemand" may decide which speed to use
                  within this range.
  current CPU frequency is 1.20 GHz.
  cpufreq stats: 2.40 GHz:0.00%, 2.40 GHz:0.00%, 2.27 GHz:0.00%, 2.13 GHz:0.00%, 2.00 GHz:0.00%, 1.87 GHz:0.00%, 1.73 GHz:0.00%, 1.60 GHz:0.00%, 1.47 GHz:0.00%, 1.33 GHz:0.00%, 1.20 GHz:100.00%

So, assuming the current policy and cpufreq stats, it's impossible to scale up over 1.20 GHz.
Even if I force with cpufreq-set. 






By curiosity, I took the kernel sources from Lucid and I compiled it. (I never had this problem with Lucid, so let's try and see what happen.) :

Linux BlackBeast-T410 2.6.32-24-generic #8 SMP Tue Oct 12 02:09:23 CEST 2010 x86_64 GNU/Linux

cpufreq-info shows me for all virtual cores :

analyzing CPU 3:
  driver: acpi-cpufreq
  CPUs which run at the same hardware frequency: 0 1 2 3
  CPUs which need to have their frequency coordinated by software: 3
  maximum transition latency: 10.0 us.
  hardware limits: 1.20 GHz - 2.40 GHz
  available frequency steps: 2.40 GHz, 2.40 GHz, 2.27 GHz, 2.13 GHz, 2.00 GHz, 1.87 GHz, 1.73 GHz, 1.60 GHz, 1.47 GHz, 1.33 GHz, 1.20 GHz
  available cpufreq governors: conservative, userspace, powersave, ondemand, performance
  current policy: frequency should be within 1.20 GHz and 2.40 GHz.
                  The governor "ondemand" may decide which speed to use
                  within this range.
  current CPU frequency is 1.20 GHz.
  cpufreq stats: 2.40 GHz:3.26%, 2.40 GHz:0.02%, 2.27 GHz:0.05%, 2.13 GHz:0.05%, 2.00 GHz:0.03%, 1.87 GHz:0.02%, 1.73 GHz:0.03%, 1.60 GHz:0.01%, 1.47 GHz:0.03%, 1.33 GHz:0.03%, 1.20 GHz:96.48%  (235)

It's far better than with the Maverick Kernel ! current policy and cpufreq stats return coherent values. The CPU scales up to 2.40 GHz with high CPU usage. So, cpufreq utils work, but not acpi-cpufreq kernel module ?!

There is also something weird... it can be reproduced with the 2 kernels :

when "/etc/init.d/cpufrequtils start" is invoked, I have got :

 * CPUFreq Utilities: Setting ondemand CPUFreq governor...                                                                                                    * CPU0...                                                                                                                                                    * CPU1...                                                                                                                                                    * CPU2...                                                                                                                                                    * CPU3...                                                                                                                                            [fail]

There is something wrong with the starting script...

Inside, I setted the values :

ENABLE="true"
GOVERNOR="ondemand"
MAX_SPEED="2400"
MIN_SPEED="1200"