How long should users expect to wait?

In the course of adding some tasty ajax activity indicators to our customer management tools I started to consider how long is long enough for a user to wait  - our users are grabbing well-indexed oracle data that effectively returns instantaneously so after first experimenting with sleep() I've settled on a nice php udf that allows me to 'sleep' for microseconds (usleep is out as I'm using a windows box) to 'convince' users that their data has been saved etc. and dissuade them from refreshing 'just to check' thus negating the server-load benefits of using ajax.

I've gone for 0.65 seconds for now and I'm just curious to know what research may have been done on this.

technorati tags:Ajax,php,UI, Oracle

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