All I can say is that I was warned but did not think it would happen to me.  Well it did and I was very lucky to have no damage.
While at Biketoberfest 2004 I fired up the bike, engine was cold, just gave a tad of throttle and a little spitback from one of the
flatslide.. Never thought anything about it.. had done this before.  Seconds later smoke coming from the faux cover.  Not good.
She was on fire.  Opened the cover to find one Uni filter completely engulfed.  Ripped it off the carb and onto the ground.  Second
filter was just starting to catch and ripped it off.  Some of the filter melted into the throat of one of the flatslides but no damage whatsoever.
Cleaned the stains with carb choke cleaner and all is well today but if I had been riding down the road and that happened my bike and
myself could have suffered much more damage.

If you've ever seen a flatslide spit back it's quite impressive.  Once you've seen the fuel / fireball spray you'll realize why
running Uni filters is not a good idea.