Basic problems include (in order of appearance):
- Compile a C code. Why Ubuntu doesn't configure well the dependent libraries for static? I try the code in other Un*x environment and works well, but in Ubuntu I had to delete the static flag and edit the headers in source code.
- Execute a CGI script under Apache (I'm not 100% sure of Ubuntu systems but I guess). If the system install a httpd.conf file with basic rules to work, you expect this work, if it doesn't, I don't like to read the manual to fix something when many other distros like Mandriva do perfectly fine the first time.
- Install updates and reboot. Sorry for the similitudes, but this is a Windows feature, why do you need to reboot after the installation of updates? I like to update if I consider necessary but I don't update every new kernel or patch not important to security or better features. Besides many updates to fix something is a bad signal of an immature release (Vista-like).
- Keyboard identification. Is possible this day to have a distro where you can't configure correctly you keyboard key-distribution? Bad.
- Unexpected crash. Why does the sound system freeze a computer? Unexplainable.
Please, if you are considering to use Ubuntu as your linux, before try another better Linux as Mandriva, Fedora, OpenSuse or Debian or ask an Ubuntu-fan to avoid the critics.