[garethsprice]

Truly great UIs aren't memorable - they just work and you don't even think about them. Elevators, gas ovens, hourglasses. If you can make a useful application with a UI as simple, intuitive and forgettable as any of those, you've succeeded.

[rprospero]

Not a UX person, so I'm a little surprised that you list the hourglass. I always thought that they had a terrible UI, mostly on account of not having a proper reset mechanism.

[rfergie]

Can't tell if you are joking or not.

The reset mechanism for an hourglass is intuitive and gives very clear feedback on whether or not the operation suceeded

[n_coats]

I agree, but I do think from a cosmetic perspective some UI's can be memorable, mainly because I've experienced some that are.