How To Answer A Programming Interview Question And Look Good Doing It 16 years ago
I guess like with everything, it's about practice. It's difficult to be good at something if you never do it. It is a bit of a pain since you never actually HAVE to do in your normal work. It is however worth practicing if you know you're going to be put in a situation where this will be an issue (such as an interview).
If you practice enough, you will get better at it and I do believe that it is certainly better to practice on your own rather than failing multiple interviews and using that as 'practice' :).