I think it will do permanent damage... seen lots of pictures on here taken with laser-damaged cameras. Typically its a stripe of pixels that will remain black (or some color) in all future pictures. If you're doing beamshots head-on (ie camera pointing in the general direction of a laser), i'd advise using an old camera you no longer really value.
Also notice that most digital cameras always have the sensor exposed whenever they are on (ie lens sticks out and its shield folded away) - both in 'preview' mode (obviously it needs to be on), but even when reviewing pictures you have just taken. So it could easily be damaged even when not actually taking a picture.