Depending of course what your definition of the word 'is' is
President Bill Clinton said something close to this while trying to explain that he had not lied when he denied having sexual relations with Monica Lewinsky: "It depends upon what the meaning of the word 'is' is..."
You can hear it here.
the kid in the teen horror movie who turns out to be possessed
A likely candidate for which teen horror film Pynchon is referencing here is Night of the Demons (1988) (aka Halloween Party). Wikipedia
patafamiliarass around here
A pun on pater familias, defined below. Avi becoming a “patafamiliarass around here” is Pynchon punning on it with “pat a familiar ass” which would be Avi’s being treated in condescending or patronizing way in a place where he's taken for granted. A "pet" of sorts, not totally unlike Chandler Platt's assistant Darren, whose rap on page 282-283 is so defiant while Darren himself remains, essentially, Platt's subservient pet.
The pater familias, also written as paterfamilias (plural patres familias), was the head of a family in ancient Rome. The paterfamilias was the oldest living male in a household, and had complete control of all family members until he died. Once the paterfamilias died the next oldest male would then have control. The pater familias was always a Roman citizen. From WIKI.
1940s-era slang for "hands" often seen in the pulp/hardboiled/noir/detective fiction of the time.
the company tambourine
The company's moneymaker. "Shake your moneymaker" is an old blues lyric, recycled, just like blues riffs, throughout the history of the blues and rock 'n' roll. Variations include "shake your tailfeather" and "shake your tambourine." 
Similarly, the rapper Eve in her 2007 song "Tambourine" used both "shake your tambourine" (shake your ass) and "shake your tambourines" (shake your tits). 
RPGs are Role-Playing Games
Ms. Cheung's bleak announcement about real life and make-believe
So what's the reference here? Who's "Ms. Cheung"? I suspect it may be a misspelling of newsperson Connie Chung's name? She was in NYC at the time of the 11 September attacks and covered it for CBS News, focusing on Cantor Fitzgerald, the Manhattan bond-and-equity-trading firm that was obliterated by the 9/11 attacks. But I can't find anything of her talking about "real life and make-believe"...
cf. p. 335: "Ms. Cheung, an English teacher who if Kugelblitz were a town would be the neighborhood scold, has announced that there shall be no more fictional reading assignments."
Edwin John "Eddie" Fisher (August 10, 1928 – September 22, 2010) was an American entertainer. He was the most successful pop singles artist of the first half of the 1950s, selling millions of records and hosting his own TV show. Fisher left his first wife, actress Debbie Reynolds, to marry Reynolds's best friend, actress Elizabeth Taylor, when Taylor's husband, film producer Mike Todd, died. This event garnered scandalous and unwelcome publicity for Fisher. He later married Connie Stevens. Fisher is the father of actresses Carrie Fisher (with Reynolds), Joely Fisher (with Stevens), and Tricia Leigh Fisher (with Stevens). From WIKI.
Goombas, known in Japan as Kuribo ("Chestnut People"), are a fictional species of sentient mushrooms from Nintendo's Mario franchise. Their appearance is based on shiitake mushrooms. Wikipedia
meet my man Ketone
In chemistry, a ketone is an organic compound with the structure RC(=O)R', where R and R' can be a variety of carbon-containing substituents. Ketones feature a carbonyl group (C=O) bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology. Examples include many sugars (ketoses) and the industrial solvent acetone. From WIKI.
Granada Asbury Park Uncertainty Question
From the lyrics of "At Long Last Love" (written by Cole Porter, popularized by Frank Sinatra)
Is it for all time or simply a lark?
Is it Granada I see or only Asbury Park?
From this page: a term used to describe a scented trail left by the fragrance wearer.
The Ray Milland Story
Ray Milland (3 January 1907 – 10 March 1986) was a Welsh actor and director. His screen career ran from 1929 to 1985, and he is best remembered for his Academy Award–winning portrayal of an alcoholic writer in The Lost Weekend (1945), a sophisticated leading man opposite a corrupt John Wayne in Reap the Wild Wind (1942), the murder-plotting husband in Dial M for Murder (1954), and as Oliver Barrett III in Love Story (1970). Milland, who was at one time Paramount Pictures highest paid actor, co-starred alongside many of the most popular actresses of the time including Gene Tierney, Grace Kelly, Lana Turner, Marlene Dietrich, Ginger Rogers, Jane Wyman, Loretta Young and Veronica Lake. From WIKI.
breaker breaker good buddy
"breaker breaker" is trucker CB-radio talk for a request to interrupt the conversations on a channel and start a new one with anyone on the channel, in this case Maxine. "Good buddy" is also common CB-radio vernacular used by truckers in addressing each other.
a.k.a., Microsoft headquarters
racks of electronic gear receding into infinity
Describing the Bleeding Edge front and back cover photograph. On the next page, Eric speaks of "Bleeding-edge developments"...
Bleeding-edge development phase
On the previous page, Pynchon describes a server farm that matches the Bleeding Edge cover photo.