Juggler works with any weapon that can be equipped in a single keypress.
That is, the 'z' key to swap weapons, or any of the numbers.
It gets a bit wierd when you have a weapon in your off-hand, because pressing a number for a shotgun when you have one in your off-hand will just swap weapons. When I'm doing a shotgun run I like to hold a shotgun in my main and my off hand. That way, you can fire, swap, fire, arm combat shotty, fire, arm double shotty, and fire. Lots of shotgun without reloading.
Even when not doing a shotgun run, I tend to go straight for juggler to take advantage of this. Plus, in a nightmare game, you have to have a weapon with knockback at the ready... You can kill a monster, walk up to his corpse, then the second he gets back up, blast him towars lava or a door frame. :)
The crashes were related to a massive amount of turns spent on one level. Kornel has fixed it now. :)