A very simple way to tell how idle your system is is to see how much time the system idle process is clocking up.

The script below checks how idle the system has been between each interval.

Code:
Break ON
   
$=SetOption("Break","ON")
   
$iIntervalCheck=30		; Check every thirty seconds.
   
$iThresholdValue=0,5,30,50,80,95
$sThresholdText="I have no time right now!", "Busy", "In use", "A little idle", "Idle", "Very Idle"
$sThresholdColour="r+", "r", "y", "y+", "g", "g+"
   
$strComputer = "."
$objWMIService = GetObject("winmgmts:\\" + $strComputer + "\root\cimv2")
If @ERROR @ERROR ": " @SERROR ? EndIf
   
; Get initial status
$iLastTime=Int(@TICKS/1000)
$iLastIdle=GetIdleSeconds()
   
$iNumCPU=GetCPUCount()
   
@TIME+" Waiting for first "+$iIntervalCheck+" second interval to expire, CPU count is "+$iNumCPU ?
While Not KBHit()
	Sleep $iIntervalCheck
	$iThisIdle=GetIdleSeconds()
	$iThisTime=Int(@TICKS/1000)
	$iDeltaIdle=$iThisIdle-$iLastIdle
	$iDeltaTime=$iThisTime-$iLastTime
	$iPercentIdle=CInt(($iDeltaIdle*100/$iDeltaTime)/$iNumCPU)
	For $i=0 to 5
		If $iPercentIdle>=$iThresholdValue[$i] $iIndex=$i EndIf
	Next

	Color $sThresholdColour[$iIndex]/n
	Chr(13)+"                                                                 "+CHR(13)
	@TIME+" Idle: "+$iPercentIdle+"% "+$sThresholdText[$iIndex]

	$iLastIdle=$iThisIdle
	$iLastTime=$iThisTime
Loop
   
Get $
Exit 0
   
Function GetIdleSeconds()
	$GetIdleSeconds=0
	$colItems = $objWMIService.ExecQuery('Select KernelModeTime from Win32_Process where Handle="0"',,48)
	For Each $objProcess in $colItems
		$GetIdleSeconds=$objProcess.KernelModeTime
		; Time is in nanoseconds - Too much!
		$GetIdleSeconds=CInt(SubStr($GetIdleSeconds,1,Len($GetIdleSeconds)-7))
		Exit 0
	Next
	Exit 1
EndFunction
   
Function GetCPUCount()
	$GetCPUCount=1
	$colItems = $objWMIService.ExecQuery('Select NumberOfProcessors from Win32_ComputerSystem',,48)
	For Each $objComputer in $colItems
		$GetCPUCount=$objComputer.NumberOfProcessors
		Exit 0
	Next
	Exit 1
EndFunction