We did it a few years ago. Basically, we sat in a boat, watched one surface for a breath of air (about 5 seconds), and then a few minutes later it happened again. After about 3 or 4 repetitions, it lost its entertainment value. Needless to say, it was not a wasted day, as the boat trip and an island picnic and a bit of snorkeling made it an enjoyable day. In my humple opinion, one of those things we were glad we did, but would probably not do again (too many other things to experience).