I've been doing The Times Su Doku since it began last year. In the process, I've hooked four members of my family and two co-workers. I even bought the computer program (best $14 I spent last year!). For generations, we've prided ourselves on doing The New York Times crossword puzzle. Now, we pride ourselves on doing the Fiendish Su Dokus (in under 30 minutes, of course). Sarah Ruth, Lafayette, California

It's not actually completing a Su Doku that particularly matters; rather, I enjoy the challenge of developing new stratgies and methods for their completion, and thus improving my own performance. I also loathe having laboriously to write the various options for each square in pencil; this, in a way, is a failure, as it takes away the beautiful efficiency of the pure intellectual solution. Name and address withheld

What a great way to do your mental push-ups before facing the day. Gary Patishnock, Laurel, Maryland

I like to do Su Doku whenever I get the chance. However, my teenage sons usually get to the paper first and they get them done a lot quicker than my old brain is able. I think they are great for mental gymnastics and equivalent to a deep meditation. Bob Wisda, Rockville, Maryland

While not exactly desperate, my fellow housewives and I keep clipboards with our current Su Dokus constantly at hand. For us, the fun is in the fiendishness, as well as the sense of accomplishment and camaraderie we feel at finishing them off. As somewhat fretful 50-somethings, our new motto could be: "A Su Doku a day keeps senility at bay." Barbara Sallay, San Diego, California

I love the new Killer Su Doku puzzles much more than the usual ones. It must be something to do with the fact that the Killers involve (albeit simple) arithmetic which must somehow appeal more to me than merely placing numbers in a grid. After all, Su Doku could be done exactly the same but with the first nine letters of the alphabet, whereas Killer Su Doku has to be done with numbers. Michelle Robinson, Matera, Italy

Addictive? Hardly. Once one understands the logic and has worked out the technique for solving it, completion is simply a matter of time. Fiendish just means "Takes Longer". And after spending a couple of days doing puzzles, the challenge, and therefore the interest, just faded away. Jim Campbell is spot on - Su Doku is no substitute for a good crossword. Evelyn Moore, Bournemouth

For Charles Frean: someone has come up with a 3D "Sudokube". You can see it at http://sudokube.freeownhost.com. Paul Taylor, Leeds

If the paper hasn't arrived by the time I leave for work then my first point of call is the newsagent. If the lad's on his round then I buy another one just for the Su Doku. To start the day without getting the brain in gear is just not on. Colin Sanders, Manchester

I don't want to spoil others' enjoyment but it must be said that not everyone is a Su Doku fan. I've started a few but could only be bothered completing one while relieving the tedium of a long air journey. It was as interesting as long division or a jigsaw puzzle: better than nothing, but not much. Why are some people immune, while others are hooked? Norman Paterson, St Andrews

It's like arranging the seating at a wedding reception. Paul Hughes, Toronto

What the hell is Su Doku? Adam Caudill, Derry

Initially, I was just a casual player, one puzzle a day. It soon became a habit, where I needed to play at least three times a day. Today, I admitted that I have a problem: I realised that Fiendish did not provide the Su Doku hit that I required. I have now progressed to Killer and this is my last communication as a civilised, sociable, human being. Many thanks to The Times, my compensation claim is on its way. Richard Atack, Stirlingshire

I have to do a Su Doku in the morning - it's like taking a shower for my brain. It helps to clean out the cobwebs and start the day. It can also be a form of meditation, helping me to relax and focus inwardly no matter what is going on around me. Oh, and it has a dark side - it can also possess me and completely take over my other priorities and drive me into an obsessive state of determined competition - with myself or with anyone nearby who is working on the same puzzle. I'm still hoping someone will manufacture a three-dimensional "Sudokube". Now that would be a challenge. Charles Frean, Bedford, Massachusetts

I mostly do Su Doku during my midday break. It makes me forget my problems and gives me a sense of achievement, but most of all I like the investigative aspect of working out why something must or must not go in a certain square. I must be a very boring person to enjoy this. I keep saying I am going to stop soon, but I'm still at it! Liz Bicheno, La Gomera, Canary Islands

Su Doku is so much fun. My brain gets more exercise doing one fiendish puzzle than it does in a full day at work. And the satisfaction you get when you've completed one, especially a tricky one, is like winning a big prize. Maybe Su Doku is the new fashion for the intelligent or, dare I say it, geeky, among us. Natalie Wehden, Nottingham

So simple and at the same time, so challenging. Su Doku is absolutely fabulous. The sheer logic of the game is something you simply can't resist, you are bound to become an addict from the very first puzzle you solve. Maria Perzy, Katowice, Poland

Su Doku is the perfect antidote to prevent the brain turning into mush during pregnancy. The best challenge is to try and guess the origin of the puzzle - ie, which newspaper it comes from. Justine Williams, London

Nothings says "I can't do crosswords" like a completed Su Doku grid. Jim Campbell, Marksbury

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