I ran across htop as I was installing software on my new Ubuntu install, and am finding it invaluable: much clearer than the standard Linux top.

I installed Ubuntu 8.04.1 on a Pentium II machine with 256MiB and was disturbed by how slowly it seemed. It turns out that it was just that bash was starting incredibly slowly. Removing the default Ubuntu ~/.bashrc fixed it. It turns out to be something in /etc/bash_completion which causes the slowdown, but I haven't figured out what yet.