Not following conventions
Here is an e-card from planet pulse that could easily tick off users. The flash new year greeting has a loading bar that looks like a conventional progress bar but only thing it goes right to the end and then jumps back to start all over again.
I shut down the browser thinking it was faulty scripting done in flash and I'm sure many users would do the same because it very much breaks the convention we are used to on the web. Think about all the hard work that would be such a waste, just because you chose the wrong load bar animation.
See the card here to see how intuitively it drives people away http://www.planet-pulse.com/php/flash/ecard.html