NimbleBit's Tiny Tower [Free] had an update land moments ago that among other things, addresses one of the more valid complaints I've seen about the game in that (previously) aside from building up your tower and keeping your store stocked there wasn't much purpose to the game. That's totally valid, as for some, the drive to simply make your tower taller isn't enough. That's where the new missions system comes in. Check it out:

Now the game has actual objectives which encourage you to have a wide variety of floors so you can stock up items to satisfy the mission requirements. You even get some free Tower Bux for your efforts. In addition, stock can be gifted in between friends, so you don't even need to have those floors in your tower to complete missions if you've got friends willing to send you some stock. Or, stock can be traded between players just for fun.

Some new UI tweaks have been added as well, to make floors with dream jobbers on them easier to spot. And, of course, it wouldn't be a Tiny Tower update without new floors and costumes.