For the hopelessly devoted Facebook gamer on your list, sure, you could just load up a gift card and give them $100 to burn through in MafiaCitySimSocialCastleFarmWars. You could also stage an intervention. Neither option is going to make both giver and recipient happy.
Instead, here are some ideas that, like the best holiday gifts for co-workers and middle-distant relatives, satisfy the obligation of buying them something while supplying a passive-aggressive appraisal of their habit. These are gifts that don't necessarily say to the recipient "I care" as much as they say to others "I tried."
If this person is a serious devotee of Facebook games, then the soundtrack to whatever they are playing probably seriously pisses off their surrounding co-workers and/or family. In-ear headphones -- aka earbuds -- are a low-cost, multipurpose and functional gift that also provides a subtle reminder that people don't want to hear them playing CityVille or Bejeweled Blitz all day long. $US9.99-$US19.99.
Self-explanatory. $US10.04 via Amazon.
Want to nudge your Facebooking friend off their Sims Social kick? Chances are they have some gaming-enabled smartphone or tablet. Giving a set of Fling joysticks encourages them to go experiment with heavier gaming fare -- and yes, in this intervention, we'll consider iPhone and Android gaming to be "heavier fare". Fling's official site maintains a spreadsheet of titles that support the stick or sticks. So give 'em a few bucks to buy one or two of those, too. $US19.95-$US29.95.
It's a good bet this person also is caffeine-addled, and if they're in charge of the office pot, that's bad business. While the continual refill is nice, it might be brewed to strong or brewed too stank. Better for everyone to be in charge of their own cup. Sure, there are more glamorous single-serve machines out there but at $US30 the Senseo still punches out a nice mug of joe with no fungus-incubating leftover grounds. $US29.99, limited time sale.
The seriously committed Facebook gamer may be someone who neglects certain chores around the house, such as child care. Kidding! But seriously, it's easy to forget about keeping Mr Snuggles' doodoo dome nice and sanitary when you're spending all goddamn evening in front of a computer screen. Why not let a robot do the work for you? ScoopFree's self-raking fortress of solitude employs disposable trays so that the pet owner never has to "see, touch or smell messy waste". It also includes a digital counter so that when police intervene they know exactly how many shits the cat(s) took in it since the last time the pan was changed, providing a useful detail for the local newspaper's horrified readership. ScoopFree offers lower-cost configurations with fewer features too. $US179.95, available online.