There is a utility called Fusion Icon that allows you to change either the
window manager or decorator on demand. When you load it, it sits in the system
tray and if you right click on it, you can change from Compiz to Metacity or any
other window manager installed. You can similarly change from GTK (Gnome) to KDE
or Emerald decorators. It is in the repositories.

I know this app well but I was hoping for a more perminant solution. Any ideas?

Compiz Fusion is very resource intensive. If performance is your goal I would
consider not using it. It works on my eeePC with 1 GB of RAM, but it slows it
down. I therefore tend to use it only on my desktop which has over 3 GBs of RAM
plus a 512 graphics card. If I want desktop effects on the eeePC then I use less
of them or run another desktop such as XFCE which is less resource hungry and
has built in compositing. I read that Gnome x.24, (the latest version) which
comes with Intrepid has a built in compositor. I have not used this feature yet
although I am running 8.10. I plan to try it out on my eeePC shortly.

I am not familiar enough with the specs of your computer to give a reason why it
bogs down with Compiz, but I would think that it might have something to do with
the amount of available RAM and/or video RAM. When Ubuntu slows down it is
usually due to excessive caching to the drive which is slower than RAM. This can
happen if your swap partition is too big and/or you are trying to do something
that is memory intensive. A large swap partition does not improve things if you
don't have the RAM to back it up. It can slow things down if it is too big
because the seek times are greater. The swap partition should be not any larger
than the RAM. If your swap file is the right size then I would look at getting
more RAM if it is lacking or if the swap partition is too large, either reduce
it or increase the RAM. If you feel that you have lots of RAM and a suitable
sized swap partion and it is still slow then I would look into whether it is
slow when doing other
resource draining tasks such as graphics editing or gaming. If not, then
perhaps Ubuntu could stand some tweaking and there are some tools to do this,
including taking advantage pre-loading which was built in with 8.04 but not
enabled by default.

This is just a shot in the dark since I don't know your system.

I am not making myself clear... Compiz works fine on my system UNLESS I
have just resumed from suspend or hibernate. That is when the slowdown
occurs. If I then kill compiz and restart it, it works fine again.

Does it happen only in Ubuntu or have you seen it
in other distros? Hibernation problems are widespread and it is suggested that
some manufacturers add proprietary extensions to acpi that may mean that they
behave not as you might expect if Linux is set up with regular acpi
implementations. I am not sure how this fits in with Compiz. I am just throwing
out an idea. Some people have kernel patches and scripts to solve some acpi
problems with certain distros or else the recommend that you unload some kernel
modules in order to fix it. It sounds like a lot of work to me.

Well, my own theory is that Compiz still needs the nvidia driver, which
is required to be unloaded manually when the system enters suspend as
the driver doesn't respond properly to the suspend request from the kernel.

Once the system is restarted the nvidia driver is reloaded manually.

When this happens, since Compiz is in use when the system enters suspend
and thus its full state and connection to the nvidia driver is stored
in memory (and thus resumed where it left off) compiz has no idea it
needs to re-establish a link to the driver (since it has been completely
unloaded and reloaded).

Ideally, a script would unload compiz and reload it after the driver in
the same way, but not having been a programmer in some time I am not
sure I can write a driver to do that.