A quick tip: really improve playback performance in the VSE by simply matching your scene’s dimensions to the media’s size. (this is more of a reminder than anything).
As pointed out by “blendervse” here ages ago - http://blendervse.wordpress.com/2010/10/30/1088p/ – Canon DSLRs actually record a HD video at 1088 pixels (not 1080 as expected). Blender of course spends computer cycles resizing every frame. So try giving your playback a boost by removing all resizing! I saw dramatic improvements even playing files from a slow old USB memeory stick.
Or if you are feeling like playing with each strip more, you can set the scene resolution to 1080, then go to each strip and change the Strip Input/Image Crop values. That is, you change the Bottom Crop value from 0 to 8. Thereby removing 8 pixels or restoring the aspect of the original media! Then you could use the script Extra Sequencer Actions to provide a copy function (strip menu/copy properties/input-image crop) for all successive strips. Just remember to select the altered strip last, then apply the copy function.
While I’m talking about matching scene sizes, don’t forget to match your frame rate too. If you see the audio strip (light blue strip) running longer or shorter than the video strip (dark blue) then you have to change the scene frame rate (*advanced tip* or add a pitch change to the audio strip).
That is check your media’s frame rate eg. 29.97fps and make sure you set the Blender scene frame rate to the same value. This makes sure that the audio length stays in sync with the video.
Video editing in Blender should go much more smoothly then
A small update, I notice that Peter Schlaile has recently introduced a patch to correct the 1088 pixel height issue. Check it out at http://lists.blender.org/pipermail/bf-blender-cvs/2013-April/055199.html you will have to grab a build after this version 56046