One of the frustrations with using various devices is that they don't always play nicely with each other. For instance, wouldn't it be nice if I could start an instant messaging conversation at work, continue it after I leave using my iPhone, and pick right up where I left off on my Mac Mini when I got home?
To achieve this, they keep your chat alive in the cloud, so Trillian knows when you switch to your iPad where you were in the conversation and can pick right up where you left off. It's a great concept, and I'm beginning to see more and more of this.
I already have this concept for email (I use Gmail) and calendaring (Google Calendar). And recently I got Things, which syncs my to-do list between my Mac, my iPhone and my iPad (though not with the cloud). Simple Note is another great example. As more and more of our content moves to the cloud, we don't need to manage where the data is and worry about keeping it synced — it's automatic.
Does Trillian's continuous client sound interesting to you? It's still in beta, and currently only available with their Windows client, but you can download it here. Be sure to select the 5.0 beta version!