One-to-many IM application like Instant News is vulnerable to spamming and other abuses.  An obvious article titled "Consumers to Marketers: Don't IM Me" discusses public opinions on IM spamming.

When it comes to delivering advertising via instant messaging (IM), marketers and broadband-service providers should take a hard look at what they're doing, according to a study from broadband-software developer BroadJump Inc. Spam is a no-no, and banner ads largely go unnoticed as consumers see the IM space as very personal.

This is a hard problem to get around without digital identify.  For example, spam filters are not accurate with only individual sentences as context.