There's a side issue to the level drain debate (on Grognardia, with my own contribution in my Friday afternoon post.) Perhaps it should be a central issue instead. I think people have a serious misunderstanding about levels.
Despite the fact that you increase your character's level by earning "experience points", levels do not represent experience.
I know there was a shift towards "level advancement represents improvement of skills" with every later edition, but it leads to ludicrous things like NPC classes for bakers , merchants and sages, or a proliferation of high-level NPCs. What levels represent are that tiny bit of heroic drive that makes a character better than normal. Expert skill is better represented another way, through time and training (which is one reason I came up with Blanc.) Earning "experience points" is an abstract measurement of seeking out and completing extraordinary adventures; the more adventurous the character is, the more likely they will rise far beyond normal humanity.
So, a wight draining a character's levels does not cause a character to forget anything. Instead, the character loses some of that extra spark, and must fight to regain it.