Wait Timers and Performance

I want to know the performance effects Wait Timers have on the system.

My workflow rule would kick off when a Case is created and then wait until a
certain picklist value is selected. When a value is selected from a picklist
in the Case, an email would fire off and the workflow would be finished. I
could have 500 or more cases in a Waiting State at a time.

So my question is; what kind of hit is the server going to experience?
We are also running Great Plains here as well which is utilized nicely.

Thanks much