With my kids we started very young. I've always read to them. Be it looking at a picture book and making up stories to go along with the pictures, or words that are in the book. I tend to use different voices and mannerisms for different characters, but that is mostly the ham in me coming out.
We also started something when the kids were 3 or 4 years old that has really solidified their love for and desire to read. In a word... bedtime.
For my kids, time for them to go to bed with the lights out has ALWAYS been 30 minutes earlier than what it should be. Here is the key. They have to go to bed with their lights out, BUT... if they want to lay in bed and read a book they get an extra half hour until the lights go out.
Any parent can testify to the fact that kids look for any reason to delay bedtime. By using this method, the kids have already been in bed for a half hour by the time the lights go out. We have very few instances of "I have to go to the bathroom..." or "I need a drink of water..." by the time the lights actually go out. After 30 minutes of laying quietly in bed reading, they are calm enough to be ready to go to sleep. OK, we also give the kids bottled water to keep at their bedside to alieve that attempt at delaying bedtime.
As the twins have gotten older it is not so much of a "treat" any more, (mostly because they are now doing homework up until bedtime if they have it) but too late, they already love to read! As for #3, his interest is definitely on track and rolling full steam ahead.
One advantage reading has given them that I notice over their friends that are not avid readers? Vocabulary. My kids have a stronger grasp on the language, its usage and a wider vocabulary than that of kids who read only under threats.