At his first birthday, it was restricted to the crib (or sleeping situations). Shortly after his second birthday we ditched it altogether. No tricks or trades, just cold turkey. (He didn't actually eat cold turkey, we just used that method.) It was much less painful for both of us than I'd expected. (If it's not so painless for you, check out MamaCheaps' link to great tips today.)
Then my second little bundle of blue came along and was pretty much born with his thumb in his mouth (which, let me tell you, can complicate delivery). His first birthday came and went with no restrictions and, with his second birthday right around the corner, I see no way to restrict! After all, it's a part of his hand. The very hands that we encourage him to use.
So what now? As with everything, there are conflicting views out there: leave him alone (see palate expander issue below), enourage other activity/keep him distracted, use old fashioned bad-tasting lotions, don't use old fashioned bad-tasting lotions...parenting is so confusing.
Any good ideas out there? Just to complicate things further, I'll reveal that he does not have a preference-- he'll take whichever thumb is most easily accessible. And yes, we see it more when he's tired, bored, hurt, or scared, but it's not limited to those times.
Ugh, if only we could let our children be...well, they'd probably need rootcanal, palate expanders, therapy, and a good hazmat-level scrub. But they'd probably need those anyway!