Don't Whisper me then!

You know those people who are always busy chatting to a hundred different people ingame? They are easily spotted as they often start whispering you with some sort of question but when you respond you don't ever hear something back. "hello?" "anyone still there?"
It seems like this guy seems to go AFK all of the time or perhaps has alot of disconnects and misses most of your returning whispers... now the most likely (as far as i can imagen) is that he/she can't handle all the simultanious whispers and chats going on, but then again: Don't whisper me if you know you won't be able to keep up the conversation!

These is this one guy in the guild who does this alot, he asks me something or just starts making small talk... so i whisper back.
Often i swing a few more chatlines into this persons direction before i figure he's too busy to answer me again or has left the keyboard. When i'm lucky i get a sort of appology long after my final chatmessage, rarely containing a response to what i actually said/asked.
Annoying? yes... but it just makes me invest less time in this person which is actually a shame, but no one enjoys talking to a brick wall. (or is there something as a brick wall fettish?)

However when you get the feeling you are missing out on things because that other person doesn't respond to your whisper things are getting a bit more frustrating for me. Perhaps you have whispered before for an invite into a raid, either from the guild or a pick up, and you don't get an answer or an invite... how long will you wait before you give up on the idea of raiding? You might even skip on other invites as you expect to join that first group.
When i ask someone "Hey, wanna join Heroic MrT?" and that person answers "I'm afraid i'll have to run it on regular first, i guess i'll find a pug for that later", should i just stop the communication there? I think it's polite to at least let that person know that we are really looking for someone who can do it on heroic... or at least some sort of confirmation that you get the message, a simple :( would already be enough.
Without a reaction he might think there are other options available, perhaps a run on regular first or a different Heroic. If shortly after i would spam guildchat if i see someone online to fill that last spot that could have been hís/hers, that might not be appreciated.

Was this a rant? Perhaps it was, but it was either this or start a rant about getting ganked by level 70 players when happily questing.
What is so damn funny on landing besides a lower level and showing how your epics can (nearly) one shot me? And then fly circles in and out of my view reach, hoping to kill me a second time.
But wait, i said i wasn't gonna start about this.. not just yet anyway.