My MySQL datafile seems to growing alarmingly

Hi Friends,
I have a MYSQL database which is currently 40GB size. Normally it grows 100 MB per day. I created a dump last saturday (16-August-2008) using mysqldump. And found that the datafile grew significantly by 10 GB more.

My question is: Did it grow due to my operation? How can deallocate the unused space? Please help me out.