Excellent.

One example that has gotten a lot of press lately, and one that many people will be able to relate to, is a status update (given the frequent twitter outages). When you are posting a status update, you want it accepted as quickly as possible, as someone might be doing it from a phone or while their wife is calling. But you also want it to be reliable. So drop it on a queue. Once it passes through the queue, the observer can handle the task of pushing it into the data store (which in a real app might involve updating the search index, etc).

On a related note, you could have the clients themselves simply observe topics which that observer publishes when it updates the data store. That way, clients aren't pounding the heck out of the database. I'll leave it up to you to decide what you want to implement.

-Dan