Recently I asked two questions on the Avid Media composer forum of problems I have been having I am sure many others editors will run across.

1. First problem was trying to move a clip down the timeline to line up with the audio track. The answer was to select the clip and then use the keys “M” & “/” to tap the clip into position.
   http://community.avid.com/forums/p/160180/808357.aspx#808357
2. Second was deleting an effect between two dissolves, Media Composer likes to delete the transition first before the effect. Answer is to select the clip first and then delete the effect.  You can use the segment mode with either the overwrite or the splice in tool.
   http://community.avid.com/forums/p/160201/808386.aspx#808386