Windows applications do not launch, or have started acting strange.

Running Crossover on recent versions of Linux (in particular Ubuntu 8.04, Hardy Heron) may generate errors or warnings such as
preloader: Warning: failed to reserve range 00000000-60000000 err:dosmem:setup_dos_mem Cannot use first megabyte for DOS address space
and may refuse to run applications, especially ones that use Win16 or DOS calls. For instance, Microsoft Word 2000 will crash after a few seconds.
The workaround is to give the command:
sudo sysctl -w vm.mmap_min_addr=0
This fixes the problem until the next time you reboot. (It also reduces security slightly.)
To avoid having to give that same command every time you reboot, also edit the file /etc/sysctl.conf with the command
sudo gedit /etc/sysctl.conf
and change the line that reads:
vm.mmap_min_addr = 65536
to:
vm.mmap_min_addr = 0
That will apply the workaround for you when the system starts.

Outlook 2003, World of Warcraft, Steam apps can't connect.

Open your package manager and install "lib32nss-mdns". Ubuntu Bug Tracker has more details.

There is no sound in my application running in Crossover.

Ubuntu 8.04 uses the PulseAudio backend, which isn't entirely compatible with Wine yet, and sometimes doesn't like Crossover. If you switch the OS back to using ALSA (https://wiki.ubuntu.com/PulseAudio) you should have audio restored to your Crossover apps.