You don't need to touch the command line in Ubuntu... really...
If you are looking for a challenge, I suggest Slackware or Gentoo (especially gentoo...)
Here is what you need to know about simple linux command line:
nano, emacs, and VI are your command line editors. aplay, play, alsamixer are for multimedia. links, links2, and lynx are for internet use
mount [device] [/mount/point]
mkdir [directory]
cp [source] [destination]
cp -r [directory] [destination]
cp -r [sourcefolder/*] [destination/subfolder/]
mv [...] [...] (same options as cp)
rm -f -r [directory or file that just won't delete, use carefully]
/dev/hda = primary master
/dev/hdb = primary slave
/dev/hdc = CDROM usually, secondary master
/dev/hdd = secondary slave
/dev/sda = usually removable drive or SCSI drive
/dev/hda1 first partition
/dev/hda2 second partition
/dev/hda5 first extanded partition
/dev/hda6 second extanded partition
/proc useful place to look for info
cat /proc/cpuinfo (check for CPU info)
echo something
echo something > tofile
echo something >> toappendtofile
dd if=infile of=outfile
these are some basic commands, enjoy.