The kid and I have worked our way up to Stargate: Universe, which is alas no longer streaming so we're having to netflix it via disks. As slow as this is, it has some cool extras on it, such as the Kino diaries (Web-only content, mostly the diaries of some of the characters, though some are clearly deleted scenes), and on disk 2: "The Daniel Jackson Introductory Collection."
In the very first episode, a civilian named "Eli" is press-ganged into the SGC owing to his math prowess. He's our audience-identification figure (And in fact he wears a shirt through the entire run of the show that literally says "You are here").
Since Eli knows nothing about the previous 13 years of Gate they bring him up to speed by putting him in a room with a bunch of DVDs. No, really. I think this was a deliberate in-joke*.
Anyway, the first one starts out "Hi. I'm doctor Daniel Jackson, and the device you see standing behind me is called a 'stargate'. First uncovered in Egypt in 1928, it was actually..." we then get a montage of Eli watching the disks, Daniel on a TV screen, Eli taking notes, and a vocal collage of various bits of overlapping Jacksonian narration. This is evidently the standard was of introducing the basics of the program to new recruits.
In the next episode, Rush says something about Ascension, and Rush gives a one-sentence explanation. Eli: "THere was nothing about that on the DVDs!" Rush: "There's a lot of DVDs."
Well, it turns out that they filmed about 8 of these things, and they're each a couple minutes long. All of them start out with a deliberately cheezy, "Hi! I'm Doctor Daniel Jackson, and today I'm here to talk to you about...." One of them explanes the Gate, another Hyperspace, another The Goauld, another The Lucian Alliance, another the Ancients, annother blah blah blah, and one that explains Ascension. All of these are kind of vaguely funny, arising from Daniel's obvious discomfort on camera. However shooting them (On three different sets, including our last-ever look at the Cheyenne Mountain gateroom before they tore the set down) is an awful lot of effort to go through if you're only going to use a couple clips and like 90 seconds of sound in a montage.
And given the fact that they actually DID film one on Ascension, and Rush's mention of "A lot of DVDs," I suspet they probably intended to use these things later on in the series to explain really involved concepts. For instance, if Ascension came up (Which it didn't, but I honestly think it would have - "Eli" meaning "Ascended" and all), I could see them sending Eli to watch another of the DVDs. This allows them to throw in a guest appearance by Shanks without breaking their own premise, and it's kinda' funny/informative as ways to info-dump exposition go.
The argument against this is that there were several times this could have come in handy ("Who are the Lucien Alliance, and why do they want to kill us?" "I don't have time for this, Eli, go watch the DVDs" "Oh, Ok") but they never used it. Which makes me think it's an idea they ditched early on for whatever reason.
Incidentally: Sam makes two appearances in the show, one in the premier, both on the same set, both in similar circumstances, bookending the first season. I strongly, strongly, strongly suspect that both appearances were shot at the same time, and then dropped in when they needed 'em.
* - When Ben Browder joined the cast of SG1, he brought himself up to speed by watching all 174 episodes of the show on DVD in one marathon 11 day session, stopping only to sleep and go to the bathroom. "My kids just threw food at me so I didn't have to get off the couch."
Kevin Long is the former head writer of Republibot, and now he's just a hired gun here to plug his own super-keen and neato website. Check it out, or he'll come to your house and savagely bore you with trivia like this. It's located here: http://www.kevin-long.com
Also: buy one of his freakin' books, already!