How big do you want -your- inventory?
Diablo's inventory was tiny. Really tiny. You had to choose between money and other items tiny.
Diablo II was better, but it was still too small. Money never stole inventory space and there was an in-game stash for each character that could hold another inventory worth of space in Lord of Destruction, but item size increased and there was more to grab. Trading became much more important for high-end gear since there was a greater chance than in D1 your gear was legit, and there were many times more items dropped.
Sure, in D2: LOD your stash was 40 spaces, your inventory 40 spaces, and the cube 8 more spaces (12 total - 4 for the cube), but when most items took 3, 4, or 6 spaces, and you kept spare potions, keys, charms, and tomes in 10-50% of your inventory, that leaves little room for loot.
"Stash the stuff" you may say. That works if I have an especially important item I wish to keep, but I barely have room for some magic find gear, my cube, gems awaiting transmuting, and a spare item or few I happen to hold there. If you're like me, you did the sanest thing and made extra characters or accounts to hold all this extra stuff, especially if you trade. Doing this was easy since accounts and characters are free to make.
This storage shortage is why in D3 I hope inventories and stashes are tremendous. Give us 100 item inventories and 200 item stashes for our sanity. (To all those who protest, I say screw all semblance of realism; I don't want to concern myself with inventory management every minute or three!) We'll help your servers by cuting down the number of mules we need to store our gear and feel less likely to want to warp to town every three minutes.
What do you think?