whats missing from a micro atx?

[OpenToSuggestions]

I was (and still am) considerng the new shuttle, which looks good but cant have any pci/pcie cards if I have a dual slot gfx card, and also is limited to a max of 3 hard drives, so I have been looking at m atx motherboards and cases.

What exactly is missing off a matx compared to a normal atx?
obviously there are less pci slots and no sli, but is anything else missing?
do they still overclock?

thanks