Powerdevil is incredibly slow switching power modes

Doesn't apply always for me. For example changing from Performance to Presentation works properly for me.

The apparently associated KDE bug suggests that this issue is related to DPMS, so please aggregate some information about your graphics hardware:

first run on a terminal
   lspci | grep VGA
now please run
   sudo lspci -v -s 00:02.0
where 00:02.0 needs to be replaced by whatever number the first output started with. Finally please post the output of the last command as comment to this report.

For me it is:
00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller (rev03)
        Subsystem: Dell Device 01bd
        Flags: bus master, fast devsel, latency 0, IRQ 16
        Memory at eff00000 (32-bit, non-prefetchable) [size=512K]
        I/O ports at eff8 [size=8]

Here is the output:

michael@michaelspc:~$ sudo lspci -v -s 01:00.0
01:00.0 VGA compatible controller: nVidia Corporation GeForce 8600M GT (rev a1)
        Subsystem: Dell Device 0228
        Flags: bus master, fast devsel, latency 0, IRQ 16
        Memory at fd000000 (32-bit, non-prefetchable) [size=16M]
        Memory at e0000000 (64-bit, prefetchable) [size=256M]
        Memory at fa000000 (64-bit, non-prefetchable) [size=32M]
        I/O ports at ef00 [size=128]
        [virtual] Expansion ROM at fea00000 [disabled] [size=128K]
        Capabilities: [60] Power Management version 2
        Capabilities: [68] Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable-
        Capabilities: [78] Express Endpoint, MSI 00
        Capabilities: [100] Virtual Channel <?>
        Capabilities: [128] Power Budgeting <?>
        Capabilities: [600] Vendor Specific Information <?>
        Kernel driver in use: nvidia
        Kernel modules: nvidiafb, nvidia

Sorry for the doublepost, but it is probably also worth mentioning that DPMS through Powerdevil does not work on my PC, as reported in https://bugs.launchpad.net/ubuntu/+source/kdebase-workspace/+bug/288318

A bunch of DPMS fixes have been committed for KDE 4.2.1.

Here is my output, I get exactly the same behaviour. I too have nvidia hardware here, but I also get this problem on another machine with ATI hardware, but I don't currently have access to that machine.

01:00.0 VGA compatible controller: nVidia Corporation G86M [GeForce 8400M GT] (rev a1)
        Subsystem: Sony Corporation Device 9005
        Flags: bus master, fast devsel, latency 0, IRQ 16
        Memory at ce000000 (32-bit, non-prefetchable) [size=16M]
        Memory at d0000000 (64-bit, prefetchable) [size=256M]
        Memory at cc000000 (64-bit, non-prefetchable) [size=32M]
        I/O ports at 2000 [size=128]
        Capabilities: [60] Power Management version 2
        Capabilities: [68] Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable-
        Capabilities: [78] Express Endpoint, MSI 00
        Capabilities: [100] Virtual Channel <?>
        Capabilities: [128] Power Budgeting <?>
        Capabilities: [600] Vendor Specific Information <?>
        Kernel driver in use: nvidia
        Kernel modules: nvidiafb, nvidia

Is it likely that the DPMS fixes mentioned above will make it into 9.04?

KDE 4.2.1 will definitely be in 9.04. The KDE included in Kubuntu 9.04 final will most likely be KDE 4.2.2.

This bug was fixed in the package kdebase-workspace - 4:4.2.1a-0ubuntu1

---------------
kdebase-workspace (4:4.2.1a-0ubuntu1) jaunty; urgency=low

  [ Jonathan Riddell]
  * New upstream release
  * Fix .install files
  * Fix docs path for powerdevil

  [ Jonathan Thomas ]
  * Add kubuntu_65_solid_dataengine_diskspace_fix.diff to fix free diskspace
   reported by the dataengine. Backported from trunk (LP: #332734)
  * Make kdebase-workspace-dev replace and conflict with the powerdevil package
   from Intrepid (LP: #334094)
  * Compress binary packages with lzma compression

 -- Nathan Handler <email address hidden> Tue, 03 Mar 2009 22:25:55 +0000

I suffer from this bug in Karmic, and have noticed that powerdevil is extremely slow shitfing profiles when system on battery, and does it at "normal" speed when system on AC power.