My introduction to computers was via a friend's 16K ZX81, way back in 1981. I just had to have one, and thankfully my parents (especially my dad, who'd done a little programming way back in the late 60's) shared my vision. I don't remember which month but I am sure it would have been January 1982 I was bought a 1K ZX81....Smiths were out of RAM packs that day and I had to wait a few weeks. I would have been 8 at the time.
How many times must I have loaded JK Greye's 1K Gamestape? Then with the RAM pack I bought Catacombs, followed by 3D Monster Maze (still a favourite) and various other games. I remember ICL had a range of cassettes with multiple 1K games on them which seemed good value. I have always been a geek and already owned a couple of cassette recorders (thanks again, dad)...I honestly thought I had invented software piracy when I hooked them together and copied tapes for friends.
I was an avid reader of Sinclair Programs, I think my dad appeared with the March 1982 issue one day when he came home from work. I learned BASIC from those and had some help from my dad writing games. My best friend at the time and me seriously looked into publishing them - I had a meeting with a guy who worked for one of the software houses and sorted out a supply of wholesale C15's and a printing company....but bottled out at actually selling anything. Some of my early games have made it onto the internet and more may in the future as I dig out my old listings and cassettes!
I must have been lucky, I never experienced RAM pack wobble. My dad was an engineer by trade and he replaced the ZX81's feet with something more sturdy and also suggested blu-tack between the RAM pack and the rear of the machine. Worked a treat!
When I got my Speccy in December '82 the ZX81 was semi-retired apart from trying to write a few games for both machines, or when Sinclair Programs or C&VG carried a juicy looking listing. Sometimes in 1986 when I upgraded to the toastrack 128K Spectrum the '81 was permanently retired...and I later discovered to my horror that my dad had used the casing for one of his home DIY projects (he was making a remote controlled boat). Dead '81

BUT....I discovered emulators circa 1990 with the Atari ST I owned at that time, and later on the PC....and even as I type a 2nd hand ZX81 is on its way to me by way of eBay. No idea if it works as I only paid £9 for it, but looking forward to finding out.
I shall never forget my '81. I learned the QWERTY layout on it, and BASIC programming gave me a wonderful grounding in logic which has stood me in good stead during my academic career and later work. It was so well designed, physically and electronically...it was so versatile - if slow! And much like a modern PC, you could add on cards to achieve virtually anything. I only ever had the RAM pack, and used it heavily for less than a year....but it did receive a LOT of use!