Not being a fan of wights (I tend to trade them away whe I can) I tend to concentrate upon wight sweeping rather than wight using. The way-point tactic can work (and can be countered as noted), but 4 thralls sweeping in a loose line through any water can kill any wight in there. They emerge slightly the worse for wear, but they can still patiently wait for their own ambush. An undamaged thrall almost always survives a wight blast.

To be honest, the lowly thrall is the unit that I believe is the least appreciated asset. They soak up so much damage while approaching that you can totally bust up a line of archers in an archer war with only a few points of loss. Also a mob of thrall can block the access to that flag for those essential 30 seconds at the end of a game. (and they are so cheap!)

(My only really good wight ambush was against a Plaid member (before I wore the Plaid) after which he swore he had learned his lesson about parking a bunch of zerks near deep water.)