Google SketchUp 8 features useful keyboard shortcuts for users making it easier and faster to create models.

Below are the 13 useful shortcut keys to use:

1.  Arc – A
2. Eraser – E
3. Select – Space bar
4. Move –     M
5. Circle – C
6. Line – L
7. Rectangle – R
8. Push/Pull – P
9. Offset – O
10. Rotate     - Q
11. Scale – S
12. Zoom Extents – Shift + Z
13. Paint Bucket – B

Reference: http://www.dummies.com/how-to/content/google-sketchup-8-for-dummies-cheat-sheet.html