John Scalzi had a blog post on this subject two days back. Basically he was saying in answer: nothing much. Give up an hour's TV (or internet surfing or gaming or similar), 5 days a week, and you can write a book in a year.
In a way he is right. Many people do just that. Plus they write while commuting in trains or waiting in queues or other odd moments. And in a year or so, you have your book written.
However, I don't think Scalzi tells the whole truth, at least not as far as most people are concerned. It's one thing to write the prerequisite number of words, it can be a much more prolonged affair to hone them to something that a publisher will buy.
Then, just when you think you have solved all problems and you have a contract...that's when you get introduced to something called the deadline. You have a contract that specifies a date by which you have to hand in your next book. And suddenly, that one hour a day begins to look like an over-optimistic time frame.
Typically, this is what happens. You have written the first book of three you have planned. You have just got a 3 book proposal accepted, with a proviso. The editor has said, we want book 1 submitted by 1st September, but we want you to cut out the dwarf character and change the setting from fairyland to 19th century Armenia. And book 2 is due 1st June next year, book 3 1st March the year after.
And you, in the first flush of success, agree to everything...
That's when those dates begin to loom large, and one hour a day begins to look sick indeed. What if, when you are halfway through book 2, you realise it's not working and you have to start again? And that is when you start searching for more time (in between keeping the boss at work happy - plus the spouse and kids at home happy, not to mention the dog walked, the garden weeded and the bath cleaned or whatever your chores are...).
And then you discover that the publisher sends you the copy edit of book 1 to correct. Two weeks work. Then later the proofs. Four days. And asks you to do some publicity. And oh, they aren't happy with book 2, could you possible insert 6 dwarves and skip the 19th century Armenian scenes entirely?
You dream of giving up the day job - but everyone tells you not to be crazy. Statistically, it is doubtful you will EVER be able to earn enough to match your day job, although if you write genre you probably have a better chance than mainstream "literary" novels.
And in the end, something has got to give. The housework. Or time with the family. That holiday at the beach (or you go and spend all the time working.) In the end most of us make sacrifices beyond an hour's TV a day. (I actually watch no TV. We don't own one.)
Is it worth it? Of course!
And my best advice to budding writers? Learn to write in small bytes. Ten minutes in the doctor's waiting room. Five minutes in a queue. In the car waiting to pick up the kids. Early in the morning before anyone else is up. Carry a netbook with you if you can. Use it. Or settle for the back of an envelope and a pencil stub if you must. Every minute means a few more lines towards meeting that deadline.
Do we give up something to write? Yes, I think so. But we gain satisfaction.