There are a lot of things about Infinite Jest that are easier to understand than most people seem to believe. I've never had a problem seeing a plot in it, for example, though a bunch of people don't see it.
One thing that I've never been entirely sure of, though, is just who is narrating this sprawling tale. The book is mostly told in a fairly tight third-person point of view (you're generally privy to the thoughts of one character at a time), but there are a number of asides that confuse this. In particular, the Don Gately sections include a number of footnotes mentioning that the words used to describe his actions and reactions are not the words that Gately himself would've used. The narrative voice is considerably more erudite than Gately would be, with the complex sentences and SAT words that are the hallmark of Wallace's style.
The obvious conclusion, then, is that it's being narrated by Hal Incandenza, who speaks in that sort of manner, and has memorized most of the OED. And that seems to make some sense, up until page 325 and footnote 127.
Page 325 is near the beginning of the Eschaton section, and describes the "trigger situation" for the game that is played on November 8, Y.D.A.U., with lots of snarky little asides and extra details. Footnote 127 reads:
A lot of these little toss-ins and embellishments are Inc amusing himself, not Otis's TRIGSIT, which is 100% all biz.
P.S. Wolf-Spiders Ruleth the Land
"Inc" here is a nickname for Hal Incandenza, so at first this seems to confirm the theory that Hal is the narrator. The phrasing of the footnote, though, and especially the Wolf-Spiders reference, marks this as Michael Pemulis speaking, which makes no sense-- if Hal's telling the story (through means unknown at some time after the main action), why is Pemulis able to add footnotes to it?
So what the hell is going on? Beats me. I suspect that this is Wallace screwing with the reader in order to make some sort of deliberate point about the artificiality of the whole narrative conceit. It would bother me more if not for the fact that I really like the main narrative voice, weird asides and all.
Have you read the 'Illuminatus' trilogy? I think it might shed some light on what's going on (I haven't read IJ, but what you describes looks like a big ole reference to it).
if Hal's telling the story (through means unknown at some time after the main action), why is Pemulis able to add footnotes to it?
A few footnotes before that one, Footnote 123 starts: "Pemulis here, dictating to Inc, who can sit there making a steeple out of his fingers and pressing it to his lip and not take notes and wait and like inscribe [sic] it anytime in the next week and get it verbatim, the smug turd." Reading through this footnote, it is clear that Pemulis and Hal were having a discussion, dissecting the Eschaton episode. This seems to discredit the notion that all of the Hal-narrated episodes were related after the main action (which I had previously believed). Why would they both be describing this episode, and to whom?
It's tempting to believe that DFW was simply screwing with the reader, but when enough (not all) little puzzling things about the text can eventually line up to yield something satisfying, it is also tempting to keep thinking about it, pressing for something more.
There is a scene toward the end, in the locker room, where it is really unclear who could be narrating. Keep an eye out for it if you are interested in the narrator question.
Another bizarre thing about footnote 123 is the fact that Pemulis either knows Hal is going to write this down, or else is coincidentally pointing out Hal's memory abilities by mentioning writing. Assuming the former, the question arises as to why. There's also a footnote from that section where they're talking about game theory and Pemulis is talking about a constant needing to be close to one, like the size of Hal's Unit. Then Hal adds an addendum, "in meters." And then Pemulis has a response to that addendum, as though he's getting the last word. It seems to me that some of the more wise-assily written passages (i.e. certain Ennet House and perhaps Joelle Van Dyne parts) may actually be written by the Peemster, because he's the one that would most likely be in the know with these people, given his involvement in drug culture.