Since updating to Lucid, a Dell Inspiron 1501 with an Radeon Xpress 200M video card had become problems after going into suspend mode. After waking up it was not possible to reactivate the screen. It stays black and the only possibility was to power off.
This will disable the kernel mode settings and message signaled interrupts. Since that, the Dell correctly wakes up again.
To add this to your boot parameters, open the file /etc/default/grub and edit the following line as root:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.modeset=0 pci=nomsi"
Than run the grub update with this command (also as root): update-grub - and your done.