Though item sockets are quite common in Diablo III, the only thing that can be socketed are the four types of gems, and there are only three types of socket values with each gem: weapons, helms, and 'other.' This seemingly leaves a lot of room for growth, and it's expected that socket bonuses will be more varied, and that more socketable objects (perhaps jewels or even some new version of runes) will be added in the game's expansion(s).