You wouldn't know this by looking at me, but I grew up without cable TV. My family had the three, sometimes two, channels that came through the antenna on the roof, and we watched movies fairly often, but we didn't have TV to the same extent that everyone else I knew did. Looking back, that was a good thing because I read more and am close to my family, but at the time, you bet I was annoyed.
Of course, I didn't know how annoyed I should be because I didn't know what I was missing. I didn't even hear of Farscape, Babylon 5, Angel, Firefly, Futurama, and a whole host of other shows until I hit university, and Buffy and Stargate were largely off the radar until then too. I saw Ghostbusters, Indiana Jones, and Star Wars IV-VI as a kid, but not Star Trek, Princess Bride, or Labyrinth. I was only vaguely aware that there were different kinds of Star Trek. I could go on, but I'm betting the geeks who did grow up with all that are dying inside right now.
Fortunately, university coincided (not entirely uncoincidentally) with unlimited internet and access to cable. I've been absorbing as much as I can ever since, but there are some shows and movies I just don't have time to watch. Wikipedia and IMDB are extraordinarily helpful, as are movie reviews, but it's amazing what you can learn from passing references, online conversations, icons, and screencaps. That's how I know that Fry and Leela have a Thing, that Kirk vs. Picard is a never-ending, often polarizing debate, and that MSTing refers to captioning movies (and fanfiction) à la Mystery Science Theater 3000. I can tell you what The 4000 and Eureka are about—I've only seen a few scattered episodes.
Fanfiction is actually a really useful way to get up to speed on a show without watching it. I'm not talking about the Suefic, badfic, or pronfic*, which I know is what a lot of people think of when they hear the term. I'm talking about stories where a character makes a different decision than on the show, where a character reflects on something that happened in the show, or where a completely new plot happens with references to a canon one. Crossovers are also good if you know one of the fandoms involved, because they let you meet a different canon in familiar surroundings. Because of fanfic, I knew the arcs of all seven seasons of Buffy before I saw more than a handful of the early episodes, I know how Dark Angel "ended", and I know who's Marvel and who's DC**.
I know that getting knowledge secondhand isn't as good as getting it firsthand, but a passing familiarity is serving me well so far. I know which shows*** I want to actually see and I know which ones I'll only ever want basic knowledge for. I can reference all kinds of geeky things in conversation, blog posts, and fiction.
One thing I'm not sure of, because of how I've approached geekdom somewhat retroactively, is how much osmosis everyone else has gotten, versus how much personal knowledge. My brain keeps trying to convince me that I'm the only person ever not to have to watch every geek film, tune in to every geek show, and read every geek novel. I know this is, as Spock would say, illogical, but I do occasionally get the impression that I'm still woefully behind everyone else. Anyone want to share their stories?
Random Friday science:
Growing crops in shipping containers
Are we making ourselves extinct?
What ended the ice age?
* Okay, maybe on that last one, but I don't read the genre so can't comment on it.
** I also know this because of this guy.
*** and books/authors. All these methods apply equally to printed stories as to filmed ones.