Show desktop in Quick Launch till Windows Vista was a handy feature which was used to minimize all the open Windows. New users would find this feature not present at the same place in Windows 7 instead it has been provided at a different location.This feature has been named as Aero Peek.
The new Show Desktop located on the bottom right of the task bar, it's not an icon, and instead it's a little bar now that is next to the Time/Date. There are 3 types of actions it can perform according to event performed.
1. Mouse Hover: Show desktop & would bring back all Windows back when mouse is taken away i.e. a preview of Desktop and see through all Running Appz on your Desktop. Use Win+Spacebar to peek to desktop.
2. Mouse Click: Minimize all Windows and show Desktop
3. Mouse Re-Click: Open all Windows again after they have been minimized by first Mouse Click.
This function can be achieved by pressing Win+D or Win+M Key combos to bring you to the Desktop. Also Quick Launch can be enabled in Windows 7 as well.
"Windows 7 Tips: Show Desktop Icon in Windows 7"
Reference : www.WindowsVJ.com