When saving figures, pick the "Bitmap" option. Metafile can be really slow to redraw, and can wind up with a screen display in Word or PowerPoint that is not what you had in Excel. The "Bitmap" will be exactly what you created; you should only worry that your image size preserves the amount of detail you want, and that the text is readable.
Excel can do the same thing with the metafiles, and I often opt to do a screen capture so I control the graphics quality (and the re-display time while editing the file).
last revised 1/22/2013