Here's my experience as the lucky odd-man-out.
Even though I'm a relatively new user (1 year), I've gone through about three "phases". I'm not a particularly active user at 900 answers. And nowadays I skip all the easy FGITW questions so I only post about 2 or 3 answers a week - mostly on specialized topics involving performance and optimization.
During my first few months on SO, these so called "residual votes" (votes on old posts) were extremely rare for me. I never really got votes on anything older than a day and I rarely ever got a lot of rep on days that I wasn't active. So in this sense it was less than a drop in the bucket.
December and February were when I found myself on the lucky receiving end of a "linked" question. Both answers were popular and went 400+, but they generated less than a vote a day each after the initial hype died down. I went on vacation for about a month in May and averaged about 2-3 upvotes a day - most of which were from my two 400+ answers. So in that sense, it was about a drop in the bucket.
Then at the end of June... was the big one. That one capped me for almost the entire month of July and now it generates more than half of my rep.
From what I've seen, the type of posts that generate a high volume of residuals are usually those that are very common problems and are highly Googleable. Unfortunately, they have mostly been "taken up" in the early days of SO.
None of my top answers are easily Googleable. So I find that popularity doesn't help much unless it reaches "epic" proportions (as least that's what Joel called it).