 <p>I'd would dinamically set the limit by constantly checking the average load/cpu usage/query time of the database... That way when there are a few users online they can do their work faster. You could set a "maximum" like twitter and if total-load > max-load-you-want maximum=150% and so on... <br><br> On one of the service-based sites i've applied this method it actually removed 60% of the spikes after i told the users about the change...</p>