You don't think Google can ever go down, be offline, but it happens and this excellent post from a network engineer explaines why in detail. If you see a blip in your numbers, make a note of the 27 minute absence of the masters of the web.
*** Highly recommend mission critical ecommerce websites use some kind of edge network such as Akami. There are two reasons: Speed and you NEVER go down.
Once you have a CDN you should offload your images to it since cache your heavy images on thousands of servers across a network like Akamai's helps speed up your site. The other advantage is your website is cached local so everything but your cart is available even if the infrastructure of the web is down.