Personally (note how I phrase it) I have come to hate Irish moss with a passion. I have used it several times now, in the recommended dosage, and each and every time there was so much gunk in my fermentation bucket that it climbed out of the airlock. I secondaried my last brew (a Belgian specialty beer) yesterday, and there were about two cups of jellified green goop in the fermenter. It clogged up the tap so I was forced to pour the beer out of the primary into the secondary fermenter, and I was unable to crop any of my precious Duvel yeast which I had intended to recover. All in all a bit of a nightmare.
On previous brews I just added a teaspoon of gelatine to the fermenter 24 hours prior to bottling or kegging, and that has always worked fine. I will stick with that. I will never use Irish moss again.
// Frank