So this came a bit as a surprise. It's all French people. I got it with
grep \"@ tweets.csv | sed -e 's/^.*"@/@/' | sed 's/ .*//' | sort | uniq -c | sort -nr | head -10
And here the Top 10 of my replies
297 @edasfr
220 @nkame
204 @fbon
177 @davidbgk
145 @notabene
145 @embruns
117 @olivierthereaux
108 @robinberjon
98 @PascaleLC
96 @rik24d
Mine: