as I saw in the olympics, is it usual in a Tae kwon Do match for the participants to cheer (what they think is) a winning move/technique, whilst they are still doing it?
In Karate matches you have to show Zan-shin (awareness/control) before during AND AFTER the technique is delivered.

I was constantly frustrated to see TKD guys cheering themselves whilst still having legs in the air, punches sticking out and while still in the opponents firing range.

Get in, score, get out, the fight ain't finished till the ref says YAME! or whatever the TKD/korean equivalent is.
Ryan!!!!!!!
thanks CapitalcTU. Like your answer, same in Karate.
I felt sorry for our young contender as he seemed upset by his result.
But, to be fair to the judges, everytime he hit his oppononent he seemed to be falling over, or there was no real "snap" to his technique. I
I hoped at the time that that was why the judges weren't scoring his techniques.
Will he look at his fight videos with a good fighting instructor, who will help him to develop and be a great contender in 2012?

Are punches not allowed? they were wearing hand mitts?

it's probably because tkd is a more flashy martial arts. Personally if i wanted to excell in kicks i'd choose muay tai over tkd any day. So it's probably a cheer just for show and flashyness, well in my opinion any ways.

To me any martial art that can be taken so lightly is more so a competition of show rather than skill.