I should add that the extent to "it all comes rushing back" is directly and inversely correlated with how long ago I wrote it, and positively correlated with how interesting/difficult the problem was to solve at the time.

Also, almost every time I go back to review code I wrote more than a year ago, my first reaction is "jesus, that's a stupid pattern/implementation. Why did I do it that way?". I've been a professional developer for about 12 years now and I suspect that will never change.