Thomas Claburn writes in InformationWeek about spim, and includes one of my thoughts about the paradoxical benefits of public IM network non-interoperability:

"Boyd also doubts that spim will ever wreak the havoc of spam. One reason is the fragmented nature of the IM networks--an AOL IM user can't talk with an MSN Messenger or Yahoo IM user. That's been a criticism of IM, but it's likely to inhibit the growth of spim. "Because the major instant-messaging networks have not worked toward any kind of public interoperability structure," he says, "it's extremely difficult to create a uniform mechanism to spim on all the networks."

But it's not impossible. Those running the IM networks are discussing greater interoperability. That could be just the incentive spimmers need."