I've been 4 times, coming up on my 5th time. There was a looooonnnggg break between the first and the second trip, and I don't remember the first trip at all.
I've been to DLR twice, and I don't remember anything from both of them. One was when I was very little (like, 5 maybe?) and the second time was when I was 8. (When DCA was still under-construction, so I haven't even been there)