Perhaps, instead of being bothered by continuity errors, we should regard it as something funny and make it into a big game as to which continuity errors are the funniest/most obvious/easiest to avoid/most essential to further a really good joke or episode.
I'm afraid I really don't buy the idea that Rachel didn't know Chandler because she dismissed him as Ross' Geeky Friend. Rachel should have vividly remembered Chandler as That Geeky Guy Who Dissed Monica So She Cut His Toe Off Before Dinner And I Had To Help Look For It EWWWWWWWWWWWWWWW! That's pretty memorable stuff, even if you are a self-absorbed little twit. BUT, I WILL let the writers off the hook as they wrote The Most Unimportant Continuity Error Which, By Existing, Allowed the Writing of a Really Good Episode.
This, by the way, is why the Chandler/Rachel meeting thing is my favorite continuity error. It isn't important, it facilitated two excellent episodes, and it damages neither character.
This is, as opposed to Serious Destruction of Important Character Personality for Cheap and Unimportant Gag Which Wasn't Even Funny, which also happens.