Once upon a time a family member broke her right wrist - and suddenly found herself learning to do all sorts of things with her left hand - and realising just how dependant she was on that working right hand.
Upon hearing about this it soon became obvious that it would be a good idea to practice ambidextrousity. Afterall, it's just teaching the brain to do with the left what it already does with the right, right?
A friend at the time said it wasn't worth the time. He considered that handed-ness was nature, not nurture, and that I might as well try to learn to breath underwater. The flaw in that logic is that no human is capable able to breathe underwater at all, ever. But humans ARE capable of being handed, and that while the brain may have a predisposition towards one side of the other, it most definately CAN be learnt.
However, most people only learn one way in their formative years and never think about it again. Or even if they do, aren't likely to put much effort into the change.
I've started to put some effort in, these are my notes and observations...
I think the first thing I learnt was brushing my teeth. This demonstrates a couple of usefull points. Firstly, that when swapping hands you have to be carefull not to compensate in other ways. For example, when brushing teeth right-handed, my head holds still, teeth bared, and arm moving predominantly from the elbow with some wrist motion also. Swapping to left hand, at first I found I tried to brush my teeth by holding the toothbrush steady in my left hand, and moving my head around! This is just how unused I was to fine motor control with my left hand. I've noticed similar compensation with mixing bowls - lefthand holds the bowl steady while righthand mixes - swap, and suddenly the left hand is doing a poor mixing attempt, while the right hand holding the bowl is also moving around to try and 'help'.
Given time and practice though, I now find that I can brush my teeth equally well with either hand.
In fact, it's more efficient - since I used to brush right handed, then switch toothbrush to my left hand to hold it while I cupped water from the tap in my right hand to rinse. I still rinse from a cupped right hand, but I no longer have to keep switching items from hand to hand.
Knife and forking is another good thing to practice handedness with, since this demonstrates that not only do you have to newly train your left hand to do stuff you normally do right-handed, but the reverse is also sometimes true - that your right hand needs to learn stuff your left hand is perfectly fine with.
I'm moderately not bad with chopsticks lefthanded (not that I'm any wonder righthanded either), and can scribble a much better line with a pen lefthanded now than I could a few years ago. But since writing is one of the most complex fine-motor-skill tasks you're likely to use, I find that this is the hardest to practice - since I almost always am writing right-handed for a reason, rather than merely just practice.
So, in conclusion...
Ambidextrousity is a usefull skill. You don't need to be able to perform multitasking stunts like 'writing two independant letters seperately with each hand'. It's sufficient merely to be able to do the same task with either hand, by your choosing. A redundant backup you might say.
To any readers of this page, please visit my Ambidextrous Challenge: Ambidextrous/Challenge
Nemo: I was, I suppose, born ambidextrous. From when I was first learning to write, I used one hang to write "Aar" and the other to write "on". I think I did it to be odd, but it stuck. The advantages to Ambidexterity are manifold, but the one I like the most is being able to type with either hand... and use the mouse with the other. If I am using a lefty's computer (my father's, for instance), I can easily sit down and use the "wrong" hand for the mouse, and not have trouble typing one-handed, either.
So, Keep practicing. It's worth it.
Matt: I'm now rather proficient at writing with my left hand, almost preferring it to my right, after going absolutely cold-turkey in the writing stakes from about 8 months ago. My English teacher scoffed, but who's laughing now. My golf has imroved since switching to playing left as well.