Cons:

Compliance issue – each push messaging technology has its own set of regulations, from minor (RSS) to heavily control (email and text messaging)
Requires mechanism to deliver content – the marketer has to use an application to send the message, from an email marketing system to RSS feeders.
Delivery can be blocked – if the marketer does not follow the regulations set forth by each push message type, the content can be refused or rejected before getting to the intended recipient.