There are two different technologies regarding desktop alerts and messaging: push and pull.
Push technology means that desktop application that receives messages (Receiver) is passive and listens to all incoming information.
Pull technology means that the Receiver constantly checks a server if there is new message.
There is no better or worse technology. Each has pros and cons.
Push technology can instantly deliver messages, but can work only via protocols that support persistent connection. And that would be fine, but these protocols are not so widely used. Due to security reasons and corporate policies these protocols are blocked too often.
Pull technology cannot deliver message instantly. Just because the Receiver has to query a server from time to time and there is some time interval between these queries. The main benefit of this technology is that it works over any protocol that does not support persistent connections, like HTTP. That means that message can be delivered in any network, no matter how it can be diversed. It can be delivered via Internet, corporate networks, VPN’s , terminal services and any remote networks. In simple words: it can be delivered anywhere.
There are desktop alert systems that works using pull technology and there are desktop alerts that works using push technologies. Choose what is more important to you: instant delivery or ability to deliver anywhere.
Most desktop alerts that used for marketing purposes: to spread information to customers (like Ding, BBC Alerts), are using pull technology. SpreadHub uses pull technology as well.