ubuntu freezes too often

Does AltGr+SysReq+R work and let you switch to tty2
Do you have another machine from which you would be able to ssh in after the crash (if it's not a kernel panic, e.g flashing numlock)? If you setup sshd and ssh in next time it crashes you may be able to get better linfo, maybe even find the cause using top,dmesg | tail
Have you looked through /var/log/syslog (ksystemlog makes this easier) any hints? (attaching syslog may help others find that hint)

dpkg -l kdebase-bin xserver-xorg xserver-xorg-core xserver-xorg-video-i128 && uname -mr
will pop out some useful version info

glxinfo's output may also be useful (specifically if you ware using dri/dri2(kms) or not).
You can disable KMS by adding "i915.modeset=0" to your kernel line, if that fixes the bug then the error is with xorg

$ dpkg -l kdebase-bin xserver-xorg xserver-xorg-core xserver-xorg-video-i128 && uname -mr
Desiderato=Unknown/Install/Remove/Purge/Hold
| Stato=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/ Err?=(nessuno)/Reinst-required (Stato,Err: maiuscolo=grave)
||/ Nome Versione Descrizione
+++-==============-==============-============================================
ii kdebase-bin 4:4.3.2-0ubunt core binaries for the KDE 4 base module
ii xserver-xorg 1:7.4+3ubuntu1 the X.Org X server
ii xserver-xorg-c 2:1.6.4-2ubunt Xorg X server - core server
ii xserver-xorg-v 1:1.3.2-1 X.Org X server -- i128 display driver
2.6.31-17-generic i686

glxinfo has a long output, if you want I will attach it here.
I will try all your suggestions as soon as possible.
By the way, I have enhanced Ubuntu's desktop effects enabled. I will also try to disable them.

Now, my system is improved a bit.

I have disabled Ubuntu desktop effects, and after some days I have enabled them again.
Ubuntu has downloaded some drivers (which ones? why?) and now the system works better. It freezes just sometimes, once each 2-3 days.

5 minutes ago Ubuntu has freezed again. AltGr+SysReq+R did not work, while AltGr+SysReq+B did.

I attach my syslog.

I have added the requested option to the kernel line:
linux /boot/vmlinuz-2.6.31-17-generic root=UUID=5119be3b-dc72-469b-a97c-f4e0defca9a0 ro quiet splash i915.modeset=0

Anyway, the problem is still present.

Sorry, it's not a problem in compiz. When compiz freezes the mouse still works. Sounds like an Xorg or driver issue (most likely driver but I'll let someone else decide that).

This issue was reported against karmic, so can you confirm if this issue exists with the most recent Lucid Lynx 10.04 Alpha release? ISO CD images are available at http://cdimage.ubuntu.com/releases/lucid/ . Thanks in advance.

This bug report has been inactive for quite some time and in the meantime Ubuntu has moved along. I hope the reported problem has been resolved in the current version of Ubuntu. If it has not and there are people willing to follow up with information collecting and testing, it is best to file a new bug report with the latest Ubuntu development version (currently 10.04, but soon 10.10), using the ubuntu-bug command if possible. Feel free to mention the bug number of this bug.

We are sorry that we are not always have the capacity to look at all reported bugs in a timely manner. Occationally we have to purge old bug reports where no progress has been made, whether it is due to reporter not being able to respond or lack of manpower on the Ubuntu side, in order to keep our list of "active" bugs current. Sorry for the inconvenience this may cause.

Here are a few tips that will increase the chances that your bug gets priority:
* Read https://wiki.ubuntu.com/X/Reporting
* Browse https://wiki.ubuntu.com/X and see if there is some relevant information for you problem
* Respond quickly to questions from triagers
* Try changing things to see if the behaviour changes, e.g.
  * A new mainline kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/?C=M;O=D (more information at https://wiki.ubuntu.com/KernelTeam/MainlineBuilds)
  * The xorg-edgers PPA: https://launchpad.net/~xorg-edgers/+archive/ppa
  * Various options in `/etc/X11/xorg.conf` (see `man intel`)
* Browse other bug reports to see if you find a similar one and provide the information that is being asked for there.

I am sorry for the long silence. I simply forgot to answer this bug any more.

The bug is still present in Lucid Lynx 10.04, even if it does not happen so often as before.
I noticed that Ubuntu freezes mainly after a standby. For example, I put my laptop in standby, then I wake it up, then I work with the laptop for some minutes (even 10-15 minutes!) then Ubuntu, suddenly, freezes, exactly as I reported above. I don't know if the two events are related, or not.

I attach the syslog. I have taken it just after the reboot of the laptop, after the last "freezing".

Thank you.

Does it still freeze if you don't suspend or hibernate and disable Compiz?

It does not free if I don't suspend and I don't hibernate.
I always use Compiz, and this seems harmless.