[DaveAK]

This may seem like an obvious question, but I'm trying to clear this up in my mind.

Scenario : Client A sends data to server. Server applies rules checking to data. Client B requests the data from Client A from the server.

OK, so if I get this right Client B "polls" the server for new data, which is similar to refreshing, but the big difference is that only the data is refreshed, not the whole page. Client side scripting takes care of rendering the page with the new data.

So if I'm right, you have to set your script up with a timer that checks the server for new data on a regular basis, i.e. it's not "event" based with the server triggering a client side function.

Did I get this right or have I just talked in circles?

So you have to set your timers to a realistic "refresh rate" depending on the size of data/server load these AJAX requests trigger. How is the best way to determine this refresh rate?