if you're using a waterfall-style printer, just make sure you let the first side properly dry before trying to run the reverse side....
was once in a rush and trying to print the second side of my banner material... and the tackiness of the ink ended up causing the banner to draw down into my friction-feed rollers and ruined my banner (and could potentially ruin your printer!)
o, and +1 to UltraFlex! great stuff!