I don't want to get too into this, but a quick test on vlad shows that you can double attack from the offhand. I unequipped my haste items and mainhand (so punch is mainhand, crush is off) and click off haste so that the offhand would hit about every 2 sec if it fired.
[Fri Apr 23 11:37:22 2010] Logging to 'eqlog.txt' is now *ON*.
[Fri Apr 23 11:37:22 2010] You punch Vlad for 130 points of damage.
[Fri Apr 23 11:37:22 2010] You try to kick Vlad, but miss!
[Fri Apr 23 11:37:23 2010] You crush Vlad for 86 points of damage.
[Fri Apr 23 11:37:23 2010] Your Frozen Savagesoul Legguards begins to glow.
[Fri Apr 23 11:37:23 2010] Vlad was hit by non-melee for 255 points of damage.
[Fri Apr 23 11:37:23 2010] Vlad shudders.
[Fri Apr 23 11:37:23 2010] You crush Vlad for 273 points of damage.
[Fri Apr 23 11:37:24 2010] You try to punch Vlad, but miss!
[Fri Apr 23 11:37:24 2010] You punch Vlad for 64 points of damage.
[Fri Apr 23 11:37:25 2010] You crush Vlad for 566 points of damage.
[Fri Apr 23 11:37:25 2010] You crush Vlad for 131 points of damage.[Fri Apr 23 11:37:27 2010] You punch Vlad for 106 points of damage.
[Fri Apr 23 11:37:27 2010] You punch Vlad for 76 points of damage.
[Fri Apr 23 11:37:27 2010] You crush Vlad for 143 points of damage.
[Fri Apr 23 11:37:27 2010] Your Frozen Savagesoul Legguards begins to glow.
[Fri Apr 23 11:37:27 2010] Vlad was hit by non-melee for 255 points of damage.
[Fri Apr 23 11:37:27 2010] Vlad shudders.
[Fri Apr 23 11:37:27 2010] You crush Vlad for 268 points of damage.[Fri Apr 23 11:37:29 2010] You crush Vlad for 276 points of damage.
[Fri Apr 23 11:37:29 2010] You punch Vlad for 130 points of damage.
[Fri Apr 23 11:37:29 2010] You punch Vlad for 130 points of damage.
[Fri Apr 23 11:37:31 2010] You crush Vlad for 273 points of damage.
[Fri Apr 23 11:37:31 2010] You kick Vlad for 8 points of damage.
[Fri Apr 23 11:37:32 2010] You punch Vlad for 130 points of damage.
[Fri Apr 23 11:37:32 2010] You punch Vlad for 121 points of damage.
[Fri Apr 23 11:37:32 2010] You crush Vlad for 228 points of damage.
[Fri Apr 23 11:37:32 2010] Your Frozen Savagesoul Legguards begins to glow.
[Fri Apr 23 11:37:32 2010] Vlad was hit by non-melee for 255 points of damage.
[Fri Apr 23 11:37:32 2010] Vlad shudders.
[Fri Apr 23 11:37:32 2010] You try to crush Vlad, but miss![Fri Apr 23 11:37:32 2010] Your Frozen Savagesoul Legguards begins to glow.
[Fri Apr 23 11:37:32 2010] Vlad was hit by non-melee for 340 points of damage.
[Fri Apr 23 11:37:32 2010] Vlad shudders.
[Fri Apr 23 11:37:34 2010] You try to crush Vlad, but miss!
[Fri Apr 23 11:37:34 2010] Your Frozen Savagesoul Legguards begins to glow.
[Fri Apr 23 11:37:34 2010] Vlad was hit by non-melee for 340 points of damage.
[Fri Apr 23 11:37:34 2010] Vlad shudders.
[Fri Apr 23 11:37:34 2010] You crush Vlad for 94 points of damage.[Fri Apr 23 11:37:34 2010] The Avatar departs.
[Fri Apr 23 11:37:34 2010] Your body screams with the power of an Avatar.
[Fri Apr 23 11:37:34 2010] You punch Vlad for 271 points of damage.
[Fri Apr 23 11:37:34 2010] You try to punch Vlad, but miss!
[Fri Apr 23 11:37:36 2010] You try to crush Vlad, but miss!
[Fri Apr 23 11:37:37 2010] You punch Vlad for 130 points of damage.
[Fri Apr 23 11:37:37 2010] You punch Vlad for 28 points of damage.
Now you've gotten me curious how 2hb vs a pair of 1h will do with panther procs, more data to come

Edit: As expected, more swings = more panther procs.