DF has a number of little rules and rulings in the various books. We use many of them regularly - whether as-written or heavily modified for simplicity.
There are some things, though, that don't come up in play. In the same mind as the easily forgotten GURPS rules, here are the ones I can find, with page references in Dungeon Fantasy 2.
Dungeon Parkour (DF2, p. 7) comes up in part - jumping, climbing - but most of the rest is the rarely/never category: balancing, diving, leg up, squeezing, skidding, etc. Much of this is me - I don't put a lot of such obstacles in my games. More of it probably my players - they'll use Levitate, or they'll avoid the obstacle entirely because some of the PCs/NPCs can't reliably transit it. I do need to put more elements in my dungeons that require such methods to get around. Speed is Armor! (DF2, p. 12) falls into this same category, but mostly because folks go heavy-armor more than light armor with Acrobatics. Even our one Swashbuckler and one of our Martial Artists wore the heaviest armor possible, so there wasn't much in the way of points placed in Acrobatics.
Trickery (DF2, p. 10) is rarely used. Mostly people either negotiate or fight, but no one really specializes in trickery. Some of the players are quite clever and can spin a believable tale, but built PCs who can't back that up ("I'm sure with Bad Temper and Easy to Read and Truthfulness I can default Fast-Talk and convince them we're their gods! Cast Gift of Tongues on me!") I suspected this is why "Good (Three-Headed) Doggie!" doesn't get used, either. We don't have that kind of druid.
"Onward to Victory!" (DF2, p. 11) has come up maybe once? But yeah, giving advice with Tactics is rare. Giving folks a bonus vs. Fright Checks or Mind Control with Leadership has never come up.
Last Ditch (DF2, p. 15) has never come up. None of it - Seeking Guidance, Praying, or conversion of altars. Even the former Rogue and NetHack players haven't tried this.
I'm pointing these out as a combination of just reflecting on my game, reminding my players what exists and is expected to be tried by PCs in the game, and for my own benefit.
Clearly, I need to have more places to balance or climb and scissoring blades to dive through, though. That's for sure.