Generally speaking, the "Add Grace Period" (AGP) should be a net positive benefit for users ...
It's a very small benefit. The numbers I've seen say that at legit registrars (as opposed to the kiting ones), about 1% of the domains are cancelled, so the AGP is roughly equivalent to a 1% decrease in the average registration fee. That means it's an order of magnitude less valuable than Tucows' recent modest price decrease. The AGP is the worst kind of insurance, because it's insuring against a low cost event. If you register the wrong domain, the most you're out is the $10 or so that you paid for it. This is completely different from the delete grace period where you stand to lose all the value you've built around a domain over many years.
Earlier today, I realized that most current AGP exploits (kiting, tasting and their kin) would seem to be in violation of section 3.4.7 of the Registrar Accreditation Agreement as I outlined below to a post to the registrar constituency.
I suppose cart hold violates 3.7.4, but the vast majority of AGP deletions are from registrars adding and deleting huge numbers of typosquats mechanically, for themselves or for sham clients where there's no third party who might not pay. The registrars who create 10 million domains a month and delete all but 23,000 of them aren't doing cart holds. Really, the best thing to do about the AGP is to get rid of it. Failing that, do something like Bob Parsons suggested and make 25 cents of the ICANN fee nonrefundable. R's, John