As an altoholic, who had hundreds of semi-active characters in City of Heroes, I really enjoy exploring new character concepts. I do not enjoy having to delete other characters to make new ones however. Please put additional character slots on the game store. I don't mind throwing you guys more money to pay for my habit, but I don't want to deal with the hassle of multiple accounts.
I would suggest $9.99 for each additional slot, or "bulk discounts" of 29.99 for 4 slots, or 49.99 for 8 slots. It may not be everybody's cup-o-tea, but I bet you make more than enough money to offset the programming costs for this feature even before taking into consideration all the folks who will buy more mule slots.