Very nice topic, I shall also share my childhood memories.
Lemmings has always been my clear favourite computer game series ever, no one game is close to it - and so it is still nowadays. Most of my memories relates to ONML, which was the most important game for me for some reason, but I remember playing original Lemmings, Lemmings 2, Lemmings 3 and even Lemmings 3D (demo version), too in the 1990s. The only thing I remember from L2 is the first level of Beach tribe, and afterwards nobody found that game from our computer anymore, what made me a little sad. From L3 I remembered best the training level but not much else. My parents recorded sometimes with a camcorder our live and in one video my big sister plays Shadow tribe level 2 of Lemmings 3. I recognized that level from that like 16-years-old-video when I played L3 last spring and it was quite a nostalgic moment.
My mom was the one who played the game with me and we wrote levelcodes down to a paper when we made progress in L1 and ONML. I'm born in 1991 and these memories are probably from -95-96. I remember clearly when we solved a snow level in Wild ranking and it came a time for me to go to sleep. I asked my mom still: "Can I have a look at the next level?" My mom clicked the next level button. The title screen of a brick level came in front of us. "Can I look closer at the level?" I asked, and we clicked so the level started and we pressed the pause button. The level looked interesting and we perhaps yet thought how to solve it, but then I went to sleep. I clearly remember that moment, so I can nowadays tell that the level was THE SILENCE OF THE LEMMINGS. Then the snow level had to be ICE SPY, even though I remembered only the tileset of that level.
I also remember that one day I went to a sauna (yeah, we Finnish people go sauna very often
http://en.wikipedia.org/wiki/Sauna), took a shower and dried myself with a towel. Then I went to the computer room and took a look at the levelcode paper, and few waterdrops still dropped from me and hit the paper, and the colour of the letters written by some red pencil spread a little. The trails are still there, but the letters are fully unterstandable, so the incidence didn't do any harm. I remember also that we were proceeding already in mid-Wicked at that time, and I guess we played ROCKY ROAD that night! (Haha, my memories focus seemingly on the all-caps titled levels...)
Finally, Havoc 5 "There's a madness in the method", was the level we got really stuck on. One day I and my mom searched the levelcodes for the rest of the Havoc levels from the Internet, and those codes (Havoc 6-20) are written in our paper with a blue ballpoint pen, all the other with some red pens. I tried many levels, but I'm quite sure that I didn't pass any of them immediately. Also, for some reason, the levelcodes were wrong for levels 18-20, so Where Lemmings Dare was the hardest level I got access to. And I tried it so many times without succeeding, I wanted so highly to see how the very difficultiest levels of ONML looked like. I remember that I thought that Havoc 20 had to be a massive brick tileset level which probably requires 100% saved. So, when one day we searched again the levelcodes from Internet and the code for Havoc 20 worked, I was really excited. It was a surprise for me that the boss level of ONML wasn't a brick level, it was a rock level !
It was though very hard.
I have all our levelcode papers still and I think that I'd never throw them away. I also drew many my own levels in papers and I have a lot of them still. The only existing level I have drawn is Where Lemmings Dare, maybe I tried to solve that level with my drawing!
When I was 11, I drew levels that I saw in my dreams. For larger maps I linked many A4-papers with adhesive tape. I have found drawings of my imaginary levels in all tilesets but Pillar and Crystal. In addition to L1 and ONML maps, I have also drawn one Lemmings Revolutions map.
We moved into a new house in 2002 and I know that I finally beated both L1 and ONML for the first time in that house, so I have been more than 11 years old at that moment (And I was the only one in my family who still played Lemmings...). Then was the long period that Lemmings didn't work in our computer anymore. When in autumn 2010 my brother helped me with DOSBox, the first games I played with it were Lemmings games (of course..)! On last winter I got a HUGE Lemmings itch again by accidentally watching custom level videos in Youtube (it was Pieuw whose miraculous levels strongly amazed me). Thanks for DOSBox (thanks my brother :>) and Abandonia (heard from my sister about this page, thanks :>) (and thank you my dad and especially my mom, for everything... :'>), for the first time of my life I played through Holiday Lemmings 1994, Lemmings 2 and Lemmings 3 in this winter-summer 2012 period, achieving some of my greatest childhood dreams ever.