And exactly how much time is that between.
Maybe the person reading back is waiting a few seconds to read back the clearence and in the couple of seconds I have been listening there hasn't been any response - or does everyone always respond immediately when you fly?
It is not easy.

Not quite. There are many dead areas or dead spots when it comes to radio transmissions. What the OP and you need to understand, the other pilot may have paused and not heard the controller or you speaking. It happens.

Blocked...

Not sure how it is in the flight levels, but down low it is not uncommon to hear half duplex conversation due to the controller broadcasting on multiple freqs and listening on another, or else due to your personal radio being unable to hear the other transmitting aircraft due to range (but ATC can hear both).

Sometimes when we hear an ATC request just have to wait a "guess" how long it would have taken somebody to respond, and jump in, otherwise may be waiting forever. If busy my greeting will be quick, e.g. tail number and level 8000.

Obviously some of these are going to result in stepping on somebody. I would be surprised if a controller thinks we don't listen, as even 99.9% of the GA guys do and 99.99% of the pros.

Center....N577WF, descend and maintain FL240.
Silence....
Center....N577WF, descend and maintain FL240
N577WF.....blocked
Center........No it wasn't blocked, WF descend and maintain FL240.
N577WF....Descend and maintain FL240.

We laughed for a while on this one!

slight topic deviation
 

Can anyone explain this?

Several times this year I've heard ATC tell another aircraft to "contact me on XYZ frequency" with XYZ being the freq I'm currently on.

Okay, makes sense. He's simul-casting on the other freq the guy he's talking to is currently on as well as the freq I'm on. So, I can hear him talking and so can the other guy.

However, I then hear the other pilot acknowledge while he's still on the other freq. After a short delay, I hear him check in on the new freq (the one I'm on).

How is that possible? (This is all VHF operations)

I can't remember all the places it's happened, but for sure it was in ANC airspace on the NoPac routes after SYA. I think it might have happened on the other side in Japanese airspace too.

Multiple days, multiple aircraft - so it's not someone accidentally transmitting on Guard one time.

I think the controller isn't aware that they already on the desired freq. Most respond before noticing they are already there. At that point, instead of coming back with some I'm already here comment, they just check in. It happened to me a couple times this week as the controllers were looking to combine freqs. They didn't know the previous controller already had me check in on it.

What I'm curious about is what information one center communicates to the next. If we are assigned a 180 heading, .76 mach and discretion to FL240, will the next controller already know that information when we check in? I understand the requirement to tell them, but it would make sense for them to talk among each other.

Here's a question for the controller: when it's really busy, and ATC says "allright, everybody just standby" before you get a chance to check in... how long do I need to wait?;) You guys never follow that up with an "OK guys, I'm caught up... GO!"

And who's the pilot with the gruff voice who always seems to follow my plane around the country to say BLOOOOCCKKED! like he lives for that opportunity.

Evidently it is the same guy that says "YOU'RE ON GUAARRRDDDD" when you listen to 121.5 enroute after each transmission.