Getting that light "streak" effect in Photoshop

I have always wanted to know how to get the "light" streaks that so so many people do now using airbrushing/blending/layering in Photoshop... I think I have a clue as to how it works, yet I have definitely not arrived at that point. I am missing something... I'm trying to achieve something like this:

http://www.deskmod.com/files/3d/files/NV-91.jpg
Located in the lower right hand side of the picture, the light "streaks" that are going down and to the right, slightly...

or

http://www.deskmod.com/core.mod?sho...n&skin_id=18758

Located in the lower left hand portion of the pic.. the lines that streak up and to the left located under the geometric one or two .. Kinda "fast" looking but a large portion is blurred. I would really like to do something like this.

Honestly I could probably figure it out over a long period of time, but is this written down somewhere, can someone gimme some clues, tutorial or steps to do this, or am I just totally out of the loop... ? Any help is much appreciated.

I would:

1. make new later on top of the layer where the effect has to go
2. make a white blob
3. set the blending mode to like overlay or something else that fits better
4. take the eraser tool with a grunge looking brush, and take off the sides a little.
5. use the smudge tool to lengthen the streak to the right shape
6. maybe even dodge some parts of it