The check-in/security process at DCA prior to 9/11 was the same as other airports, as others have stated.

Line length was a mixed bag. For about 9 months, I did a monday/friday commute from DCA (on DL, in the temporary terminal). The lines would often be long on the DL side, but if you were smart you could go up the US side and save a bunch of time (at least during the hours I dealt with it). The other reason for using the US side was that the rent-a-cops on the DL side frequently made you turn on your computer, while those on the US sided did not.

As an elite, I see very little difference in time to clear security from then to now (unless using the terminal NW is in, that's always bad).

I will say that the TSA folks are ruder and lazier than the rent-a-cops used to be.