Lubuntu 11.04 has a tool called lxkeymap to easily switch to another keyboard layout , but there was no way to assign a keyboard shortcut to switch back and forth between two or more keyboard layouts using lxkeymap.
Never memorize something that you can look up. -- Albert Einstein
'phillw' on #lubuntu (irc.freenode.net) pointed me to this post on ubuntu forums.
To switch between 'standard' QWERTY and DVORAK layouts:
setxkbmap -option grp:alt_shift_toggle us,dvorak
This assigns ALT+SHIFT keyboard shortcut to switching layout between QWERTY and DVORAK.