If I was to get a pretty valuable link. When does that link start to affect my SERP's? As soon as google crawls the page you link is on? or As soon as google caches the page you link is on?
You might see a small effect once that page is cached, but the full effect of the link will happen after the link ages. So it might be a few months. Also, if the link is new on that page, google should cache the page once it crawls it.
Every thing will make sense once the google dance has finished. This takes all new and old links into consideration.
In Google's last webmaster chat in October , Google mentioned that there are about 200 factors in their algorithm. That means having that one additional link from a trusted website has to factored with all the other algorithm determinants they have. We got a link from NY Times, and we got a lot of traffic from them. But it didn't really boost our already good rankings. Like we did not go from #8 to #3 in the search rankings for our main term. And they've linked to us twice already Don't expect a boost just from getting a valuable link. Get more and over time -- and that's the key word: OVER TIME -- your rankings will improve. Getting a link from CNN or NY Times or Washington Post is not like getting a magic pill where your rankings get a huge boost immediately. If you have further questions: please feel free to send a PM (Private Message) and i will help you.