Diablo III has been out for nearly a week and a good number of players have managed to make their way to the Inferno difficulty. Though their experience has been limited, some of them have voiced their concerns about the game's itemization and gems.
One player complained (in the usual hyperbolic manner) that "gems are near useless," as they take up a single affix and that there's no way to add sockets to existing items through artisans. "Go ahead and call me wrong, fanbois," he wrote. "But in 2 months you'll see that I spoke the truth."
This prophet was quickly answered by Bashiok, who correctly informed him that sockets take up a single affix regardless of the number of sockets on an item.
As items can’t roll two of the same stat (although hybrid affixes can overlap) a socket allows you to stack more of a specific stat. So even if you reach the upper limit of a specific stat on an item, with a socket you can overcome that limitation. Want to really stack VIT? Even if you’re hitting an upper limit of just straight affixes rolling on an item, you can add more VIT if the item has sockets.
Oh… and regardless of how many sockets you have, it only counts as a single affix. If an item rolls up 2 or 3 sockets, that still only accounts for a single affix spot on the item. An item rolling up sockets can absolutely be better than affixes.
…
So items will have an affix limit. Like “a rare of this level can only roll up 4 affixes max”. Gem sockets, regardless of how many, only account for one of those 4 affixes. (in this hypothetical situation in which this particular rare is limited to 4) So this item rolls up +MF, and they’re boots so +movement speed, and +Int and then also rolls two gem sockets. So that’s the 4 affix limit.
Bashiok also add that as gems can simply be recycled, there will eventually be a system in place to provide users with a 'gem sink' to discard their gems, should it be necessary.