^ In the Pbat's it is implemented that and buying large stacks from the merchant works also.
Folks have mentioned it elsewhere, if folks here haven't, ah, noticed. You can rightclick and hold on items in an NPC shop to buy large stacks. If you pick up a stack already in your inventory, and do the click'n'hold, it'll add to the existing stack. Only thing click and hold doesn't work with in th'leaked version, from what I've read, is crafting.
Repeat click would be most useful for most of the swords, and varying non-auto ranged weapons (bow, 'rangs). Toggling repeat click would probably be most useful for mining, but less so for combat -- timing your attacks, especially with the slower weapons or th'rangs, is a major combat multiplier, from what I've been seeing.
In other news, I just recently saw someone rapid-toggle between boomerangs and get more than one in the air at the same time. Might be interesting thing to do if you've got a few spare chakram/flamarangs.