The tracking difficulty depends on the angle of the laser to the plane. If the laser is aimed at an approaching plane from the front (in line with the approach path), there is very little apparent motion. Airliners typically fly a 3 degree glideslope and are rock solid stable unless there's a lot of turbulence. Trying to hit one from an angle would be a lot more difficult, but still easier than what anti-aircraft gunners have done for generations. However, an angle shot would decrease the chances that you'd hit the crew in the eyes.

I'm beginning to wonder just how effective this tactic would be in downing an airliner. Airliners have two pilots and either of them can land the plane. Many modern airliners can land automatically using the autopilot. During an approach, I suspect one pilot would be looking outside while the other would be monitoring the approach on the instruments. A laser might dazzle or blind the pilot who was looking outside but I doubt it'd have an effect on the pilot monitoring the instruments. If I were in the cockpit monitoring the approach and the other pilot said he was blinded, I'd either break off the approach or continue on instruments until the plane was at the decision point (typically a couple hundred feet high on an ILS approach), then land visually. By that time, you'd probably be past the laser and out of danger. Either that, or I'd let the autopilot land the plane.