I'd put the debounce BEFORE the nested While:Wend as so...
Code:
IF PORTB.0 = 0
    TOGGLE PORTB.1 ' or PORTB.1=PORTB.1 ^1
    PAUSE 50 ' debounce delay
    WHILE PORTB.0=0 : WEND ' wait 'till button is released
    ENDIF
Otherwise you're not debouncing the original Button-Press and risk running straight through the button-release code.