The DMG, Section by Section, Part 19: Spell Explanations – Magic-Users

Comprehend Languages
I found it interesting that this can be reversed and cast on a scroll to make it unreadable, though casting the unreversed version of this spell twice on such a scroll will make it readable again.

Enlarge
Apparently Gary's players tried to kill opponents by enlarging them inside their armor, but Gary says that their armor will either come loose (if secured with buckles and straps) or be ruined (in the case of chain mail) rather than kill an enlarged subject of this spell; even clothes are assumed to "split away during growth." I would have thought that Gary would have just had what a subject of this spell was wearing grow with the subject, but leave it to Gary to surprise me, right?

Tenser's Floating Disc
I don't know why Gary's such a kill-joy with this particular spell. First he stipulates clearly that no Magic-User can begin play knowing this spell or Nystul's Magic Aura, and then he bans Magic-Users from riding the Disc. Lame. (Though I think Gary's reasoning for banning these two spells may have been to allow players to choose a spell on a result of 10 on the beginning spell tables. Still.)

Unseen Servant
This is the spell my players have played around with the most, stretching the limits of how much they can communicate with an inanimate force (being able to command it clearly means that some amount of communication is possible, I've ruled). Gary stipulates that this force has no shape and therefore cannot be clothed.

Web
I hadn't ever realized that this spell requires at least two anchor points or the web will collapse in on and get tangled up with itself. I hadn't ever really thought about that, but it makes good sense.

Wizard Lock
I also hadn't realized that casters could freely pass through their own Wizard Locks. This has interesting possibilities if you want to take magic in the direction of different flavors of the same spells. (Brendan, I'm thinking of you here.)

Rary's Mnemonic Enhancer
I hadn't realized that this was in 1e as well as 2e. It came up in a previous discussion on this blog. (I prefer any one of my solutions, for the record, though the existence of this spell does settle what Gary thought about the issue.)

Wall of Force
This spell's commentary is interesting because Gary discusses two specific ways to defeat it, much the same way that prismatic spheres in AD&D and prismatic walls in Arduin are handled. These magical barriers that require specific, sometimes (especially with Arduin) non-sensical, unrelated magical keys fascinate me and seem under-utilized in the D&D I read about and play.