I agree with Gonzo - I've found it's mainly the Brits who get agitated about it.
It took me 5 goes with one guy once to get the read back - he just kept repeating the ATIS letter.
Don't upset the only person who is going to give you start up clearance!!!
Off topic - why do pilots take headings , levels etc and fly what you instruct them to - but seem to think that a assigned speed is some sort of advisory thing?!!
louby