Loose Threads:

Could those three boys that Helen doesn't want another incident like possibly be Joey, Jeffy, and Jamie?

Who is Caroline Fishback?

What post is Helen running for in the Library Board elections?

Do the Gupties ever complain about what Daria did to their kids?

Why does Jane know how to by-pass a parental lock on a TV?
--- Jane might know how to circumvent the channel blocking function if her family uses it to lock out scrambled channels so they can channel surf more readily. Of course, if Lawndale has a cable provider like TCI, they probably juggle the channels every 6-9 months, so you need to redo the blocked channels. Thus, Jane might have a legitimate reason for knowing how to remove the channel blocks. - Comixboy

Notables:

The title is obviously a baseball reference, specifically to the practice of pinch hitting.

When Mr. DeMartino tells Brittany that, despite a total lack of insight, she sometimes stumbles onto an interesting answer; Sherlock Holmes once said the same thing to Dr Watson: "...in noting your fallacies, I was occasionally guided toward the truth."

Quinn makes a nasty face at Daria (in school no less). Guess she's never had anyone tell her that old saw about it freezing like that.

Quinn shows just how she picks dates in this episode.

Daria is really procrastinating about her history term paper.

Quinn is a really bad liar.

Doris Doright is a reference to Dudly Doright, one of the characters from Rocky and Bullwinkle, a Canadian Mountie who is well meaning but pretty ham-handed.

One of Helen's goals is to break through her firms glass ceiling, something she is well on her way to doing after being put on the partnership fast-track in "Psycho Therapy" She only seems occasionally to succeed at the first goal, however.

Deena Decker has her target market pretty well pegged. She must get a lot of the "stressed-mom-and-teen" market.

We see Jane in her running outfit instead of her usual one.

Daria calls Mrs. Guptie Mrs. Kewpie at first. Kewpie dolls are a fairly common prize you can win at those little games in carnivals, and are meant to be (sickeningly) cute.

Skyler and Quinn are a bit dressed down for Chez Pierre. Their table is also the only one with a candle instead of a lamp.

Dinner for two, no wine, runs $86.75 at Chez Pierre.

The Gupties have a Christmas wreath up on the door.

We find out Jane has a sister named Summer, who has kids.

Jane's comment about them making up the story about aliens living under the north pole isn't quite accurate, as that (or variations thereof) is a not uncommon feature of various conspiracy theories.

This show has the best ending (of the season) of any Daria episode.

Mistakes:

When Helen takes the clothes in to Quinn's room, there's a white dress on the bed, but when she puts the clothes down on the bed it isn't there.

During the entire scene in Quinn's room, nothing at all (including Quinn and Helen) reflects in the mirrors.

The scheduled time for discussing current events was 8:15 but the clock on the wall said 7:20. Also, when Daria moves snack time to 8:15 the clock in the kitchen says 9:00 (or 11:45).

The announcer on the Forecast Channel said there would be a low of 41 degrees but the five day forecast doesn't have any "lows" less than fifty. If this forecast refers to Lawndale, it may also contradict with Quinn's statement that it's "almost summer".

Jane's leotards (whatever) are missing for one scene while they are telling the kids stories.

After Daria gets her paper back, the halls are very empty for being in-between classes.

The record is scratched in different places when Tad and Tricia sing "I can hope..." and when they sing "I am cool...".

Double Meanings:

Daria is watching Sick Sad World, and Quinn is painting her toenails.  SSW is about "G-string Grandmas"
Quinn:  Ew, gross!
Daria:  For once, we're in total agreement

The obvious one here is that Quinn is talking about her nails (her next line is about how awful that color looks) and Daria is talking about Sick Sad World.  However, since when does Daria pass up a chance to insult her sister?  Daria could be referring to Quinn's feet, or even her habit of toenail painting.