Good point - I'd never considered before as I'm something of a Nub when it comes to running UT with a BarbHowl every 10 or so seconds since howl doesn't affect ubers.
This is good, because your target Uber wont run off with the rest of the minions.
Also, because ubers are immune to howl, you wont overwrite your curse you just cast on him. (Amp Damage|Decrepify|or Lifetap.)
Seconded. It makes D Key runs are breeze.I love howl, though. I wish all of my barbs came with a slvl +30 howl.