I noticed it, especially when you're starting the race or getting boosts

Really!?

I like the HD rumble in Mario Kart. It's subtle but it gives you different sensations for different scenarios. The feedback you get when playing the F-Zero tracks is really cool because you are almost constantly boosting and the Joy-Con rumble feels a bit like waves going through your hands.

It's subtle but nice. Not a game changer (though to be fair Mario Kart is the only game I own with HD rumble support).

Blaster Master Zero's demo is out today, and that game has apparently okayish HD rumble. Anyone tried it yet?

My Switch is still in Sweden with my nephew so I can't test it.

After over a month of testing I can say that this is the best rumble put in any controller. If you don't like those kind of features you probably won't fall in love with HD rumble, otherwise it's really great. Not to mention that in Mario Kart 8 it makes FLIPPING SOUNDS! It actually sounds like tyre screeching when you collect a coin and it blew my mind.

I just read that at reddit: 
https://www.reddit.com/r/NintendoSwitch/comments/697kn7/joycon_hd_rumble_coin_noise_on_mario_kart_8_deluxe/
Interesting posts there

It does sound like the linear actuators are trying to mimic a speaker.
Think I read somewhere that they used sounds as inputs for the vibrations.

You are right. The HD Rumble makes the sound of the coin. You can clearly hear it if you mute your tv or whatever.

Yup, it's cool! ^^

People shouldn't expect a reinvention of the wheel, though. It's an evolution of regular rumble, nothing more, but also nothing less. It definitely feels better.

The game I'd really look out for is ARMS.

I hope they deliver a nice springy feel when using the joy con to deliver certain punches + rumble for telling where you've been hit and if your block is successful.

Apart from that the only game I'd figure will use it to any interesting impact would be Mario Odyssey

Is it like the swoosh sound captured here?

https://www.youtube.com/watch?v=FpRGndZtlgY

Argghh, just one more week till I am back with my Switchy

ARMS might have it, just don't know how effective they'll be when you are moving your own arms around. Like I mentioned in the OP I did not notice if the fighting minigames had or not HD rumble. Would expect the same thing to happen with ARMS.