Years and years ago, I typed mine into a spreadsheet on the computer. I printed it out and put it in a 3-ring binder with a bunch of other information. For a long time, I was good about updating it, and reprinting occasionally. (I even had a column for "Christmas card list" and could sort and print just those to make it easy!) But as life got busier and busier, I started just crossing out and writing in new addresses. Eventually, we had hard drive issues and lost a lot of old files - that one included...and instead of re-doing it on the new computer, I just kept tucking in slips of paper, adding on the backs of pages, etc. - until now, most of the pages aren't even really attached.
I definitely need to follow your advice!