I voted "warm" but... in practice it's somewhere between "warm" and "hot."
I don't usually keep cups on top of my machine. In fact, I haven't had the top cover on my machine for awhile so that I can experiment with some things.

Oftentimes, however, I'll place the demitasse upside-down under the stream of water during the flush to heat it up. Flip it over to fill after I prep the puck and start the shot. It's toasty warm and still dry inside.
I tend to prefer a shot after it has cooled a little so shots pulled into cold'ish cups don't usually bother me.

This is one of my HOT BUTTONS.......

For me, cold or luke warm coffee serving-ware affects the whole experience to the extreme negative. Flavor, in my opinion, does not stand alone as the only issue when the coffee is served in cold containers. Obviously, too hot and the flavor components are killed off. But if I want espresso served anything less than hot, I'll be starting out with the intention of making an iced drink. I've never been satisfied with the warming area on most machines, and almost always use a hot water soak to rinse from the machine tap.

Usually I just let the cups sit on the warming tray above the boiler while the machine heats up for about an hour, so I voted warm. If I use the same cup for the next shots, I'll wash the cup and then heat it with boiler water while grinding and tamping. I don't know why but I also keep my glass Pavinas on the tray, but they keep the coffee hotter than I like it without even heating the cups. I guess it's more to keep them all in one place. I've seen others mention the same thing about the Bodum double walled cups, and I rarely use them for straight shots anymore. They do look really nice, though.

I like my cups hot (probably would be classified as very hot for some, but I vote "hot"). I often nuke my drip coffee cups prior to pouring coffee in them- or in the absence of a microwave - fill them with hot tap water while the coffee brews. My two favorite drip cups, both of which are both large on volume and very thick, are serious heat sinks if not warmed-up and will cool a cup of coffee down to luke warm in less than a minute if they're not pre-heated.

Espresso/Cap cups will get the machine top warming and sit with hot water from the machine in them until just before a pull.

I will say hot, but I do not flush water into the cups. The cup warmer on my A3 gets the cups quite hot on its own, around 150F if I remember correctly. When using the lever machine, I will fill my demi about half full of water and let it sit while I prepare my portafilter. When making a cappa, I put around 2 ounces of water in cup to preheat it (assuming they are starting from room temperature).

If the cups are blazing hot, I do not like it. I think the cup needs to be hot enough to not shock the espresso when pulled into the cup but cool enough to cool the drink to a sip-able temperature 20 seconds after the shot is pulled. I don't want to burn my lips or tongue but I don't want the shot sitting very long before I consume it. I have been known to gulp a shot the second it finishes the pull just to drink a 100% crema shot. It is an interesting taste sensation but I cannot taste anything for another 2 days because I boiled my taste buds.

I voted 'Hot'. I always preheat my cups with brew water while I grind and build my shot. If I am going to make a pair of cappuccinos, they get filled with water and I hit the "beverage" button on the microwave for two drinks. For Americanos, a full cup, "beverage" button, dump about half the water and pull the shot on top. For Bodum double walls, I never heat them and they sit 'cold' in the cupboard.

If I make a press pot, I try to use any left over kettle water to warm my cup while the coffee steeps. At work, I use the hot water tap on the drip brewer to preheat my coffee mug (though I never drink the office coffee ).

I can't speak to "shocking" in a room temperature cup (although I think I've tasted it by adding espresso to milkshakes), and I don't care for a 'very hot' cup. I do tend to take my time drinking most beverages, so I like to extend that time a bit by not having the cup sink the heat from the beverage.

I've seen 5 minutes banted about as the recommended time for consuming a cup of coffee. No problem on the 'spro, but for a press pot or even an Americano, that's a little short for me.

HB wrote:PS: Mark at Counter Counter Culture is into iced Americanos, I'll ask him to weigh in on the necessary wait time before pouring the espresso into his ice water filled Bodum mug...

Hmmm, do share.

HB wrote:I'm curious: At what temperature difference does the espresso get "shocked"? I've noticed it with hot fresh brewed tea poured over ice (cloudy and bitter), but never noticed it for espressos poured into a room temperature cup.

PS: Mark at Counter Counter Culture is into iced Americanos, I'll ask him to weigh in on the necessary wait time before pouring the espresso into his ice water filled Bodum mug...

Good question and one I cannot answer. I have simply noticed a difference in the flavor/texture of the drink. When the cup is warm to the touch or hotter I think there is a difference. The cup gets a bitter twinge in the finish and the mouth feel is thinner when the cup is room temperature or cooler. I also must point out that I have never tried any kind of blind cupping or study to prove it, just an observation I have made over time.

During the summer, I make iced coffee/mochas using espresso. When I prepare my shot, I pull it into a slightly warmed cup allowing the shot to run down the side of the glass to gently cool the shot. Then I add some sugar to a few ounces of milk, hit it with the frothing wand to slightly warm the milk and dissolve the sugar (maybe 90-100F?). Then that goes into the shot, then cold milk, then ice. I think I get a better drink. When I pull the shot over ice, it gets bitter and astringent. Then again, I may be full of it and if I were to blind cup two drinks made my way and pulled into ice I may not be able to pick out which is which, but I think I could. It is like tempering your eggs when making a hollandaise or custard but in reverse. I start with a hot item and slowly lower the temperature.