If the author of The Salvation War knows anything incredibly well, it would be his military hardware and pop culture.
There are several characters whose names reference members' screen names or actual names from the Stardestroyer.net forums (trolls and banned forumers "drafted" into the demonic ranks were commonplace as foot soldiers or lesser officers).
There's also kitten, who aside from the telepathy is inspired by a real person, down to the lack of capitalization in her name; the original Armageddon??? thread actually has a post where one of the board members informed the author of kitten's existence and traits, which were mostly imported into the story.
Private Joanna Cassidy, owner of "ample" breasts which were, according to Aeanas, "unappealing things, the breasts of a peasant woman with a litter of babes to feed" just happens to have the same name as the actress who, among other things, voiced the infamously busty Jessica Rabbit.
The description of Memnon as he attacks a group of al-Qaeda members is a bit blatant...
"What we still don't know." Underlined and highlighted several times was "How to target another universe from the outside." Believe me, Aperture Science has their people in here a few times a day, hoping that we'll be able to come up with something.
Dale Brown's Mclanahans are seen in chapter 3 of Pantheocide checking up on a dead relative.
An author named Turtleshell starts writing alternate histories about the war against Hell going differently, starting from the little things (i.e. had Abigor not left his naga behind but instead used them to create tactical portals). In the same chapter, Robert E. Lee wonders what would have happened if he'd had access to modern command and control equipment... "Oddly, he thought, at least half of them would never have been fought at all."
The two police officers who first find Lemuel and Maion are named after the main characters of Adam-12.
Caesar paraphrases the St. Crispin's Day speech, though he's congratulating his men after a battle rather than getting them inspired before going into one.
When asked if the Targeteer's name, finally revealed after 155 chapters of TSW, was one of the only two historical figures to be introduced in Pantheocide, the author replied, "No, this is just a tip-of-the-hat to an old friend who never quite got the recognition he deserved."
The MythBusters show up in Chapter Seventy-Nine of Pantheocide. Jamie is very interested in the demolition involved in blowing up the gates to the Eternal City.
There's a ship captain by the name of Reynolds who commands a destroyer. There are also pits reserved (in Hell) for "Some network television executives. The ones who cancelled Firefly." Stuart himself has admitted he's a Firefly fan.
In Armageddon???, General Petraeus asks some Russian engineers to build a literal highway to hell.
Caesar's assistants in Hell when the readers first meet him are called Titus Pullo and Lucius Vorenus. Hell, the PFLH manages to get the series on DVD sent down with a travel-size player, so they can see their own depictions.