Ugg..I'm facing the same decision. First kid, 5 months old. I can't figure out if it is the right time to do this, but I think it has to happen sooner or later.

Here's what we did:

let her cry for 5 minutes, go in for 1 minute to soothe her, then leave. repeat.

after a few days, increase the time by a few minutes. etc.

It's SO difficult, like it's tears out your insides. But worth it in the long run. And the sooner the better.

We tried a couple of different times, a few months apart, starting at 8 months or so. First time we would go in every five minutes. Took a couple of days. Then we did a long trip and we took a few steps back. When we got back, we just let her cry. She probably cried no more than 20 minutes at a stretch? Also took a couple of days. When she's not sick she now easier to put down, she goes to bed earlier, and she generally goes through to the early morning. She's woken up as late as 7am before. If she gets up at 5:30 I bring her to bed with me for a little while more. Sometimes she'll go back to sleep. Other times she plays. But its a darn sight better than her 12am, 3am and 5:30am wake ups, usually coming to our bed by 3 if not earlier.

I've known of other kids cry for much longer. The longest I've heard for a parent who held out and was succesful was for a kid at 14 months - 8 hours the first night (don't know if this was off and on or non stop), 4 hours the second night, 2 the third, and then golden bliss thereafter. She said her husband almost had to tie her down but it was way worth it.