Actor Allusion: Gwen has a poster of The Go-Gos and it's established that she's a fan of the group. Gwen was voiced by Jane Wedlin, rhythm guitarist of The Go Go's.
One episode, Posey, played by Vicki Lewis, tries to "find herself" by meditating. At point, her spirit guide - a ghost version of her - says she has to walk across an incredibly long bridge, then say they can take her Miata instead. In the season two Christmas episode of Newsradio, Beth (Lewis) and every one in the office is given a Mazda MX-5 Miata.
Fan Nickname: The businessman who repeatedly whispers "penis" to people is officially called the Concerned Businessman, but most people just call him the Penis Pervert.
Tom Kenny was also almost every unnamed male character on the show. At least half of them. Including an actor who played an Ewok in Return of the Jedi who sounds exactly like SpongeBob. Tom Kenny was to this show what Billy West is to...a lot of animated shows of the 1990s, 2000s, and now (read: he voices a lot of characters).
Gwen is Jane Weidlin of The Go-Go's (which explains why Gwen's favorite band is The Go Gos)
Posey is Vicki Lewis. Her voice for Posey was a case of Throw It In, as she came into the recordings from the dentist's sounding really weird from being under anesthesia. Fortunately, she was able to recreate it for future episodes.
Keep Circulating the Tapes: Even though the show is out on DVD, all the licensed music has been overdubbed with generic music, so if you have any episodes from when it aired on The WB!, [adult swim], or TBS, then keep those (whether you taped from a VCR, a recordable DVD player, have them DVR'd, or you downloaded them from a torrent site). YouTube has the [adult swim] cut of the series with the licensed music, so catch them before they're pulled for copyright violations.
Screwed by the Network: This is one of the best examples of truly screwed by the network. Mission Hill was essentially doomed to fail almost a year before the show aired thanks to The WB. According to Bill Oakley, the show's staff was told that their upfronts "didn't matter", and so Oakley and Weinstein submitted a poorly edited two minute long clip. Later, during The WB's schedule presentation, they failed to air anything about Mission Hill. For a whole seven months before the show's premier, journalists knew nothing about the show except the bad two minute upfront that was submitted, leading to nearly universally bad reviews.
Even worse, the WB immediately scheduled Mission Hill for the "death slot" - Friday at 8PM. The producers once lamented this decision, stating that Friday evening was "exactly the time the target audience was trying to not be at home watching WB." It aired before a black sitcom block consisting of The Wayans Bros., The Jamie Foxx Show and The Steve Harvey Show, a completely polar opposite audience than what Mission Hill was aimed at. The show was put on hiatus after only two episodes. A full ten months later, the show was aired again, this time making it to five episodes before it was cancelled for good.
What Could Have Been and Unfinished Episode: There were 18 planned episodes, with two of them ("Freaky Weekend" and "Pretty In Pink") having partial animatics and voice recording finished, and the other three ("Death Of A Yale Man", "How To Get Head In Advertising" and "I Was A Teenage Pornstar") fully scripted. The series was cancelled before any of them could be finished. The remaining material can be found in various places online. If the show hadn't been canceled, viewers would have seen Kevin finally standing up to his parents ("Bye, Bye Nerdie" or "I Was a Teenaged Porn Star") and Ron's Waterbed Store (which was seized by the government after Ron got busted on tax evasion) would have been taken over by a man who looks like Ron, but is Southern ("Crap Gets in Your Eyes" or "Pretty in Pink").