Let's say you have received some quality links to your site in the past couple of days and Yahoo for instance has deemed your site worthy of higher rankings in their SERPs. Would you still have to wait for them to update their database to see the higher rankings and how long does it take? It seems this is the case with MSN.com. It's like they don't make ANY changes for about once a week.
No, I'm saying is there a waiting period between when they decide to move your site in the SERPs and when it actually happens, because they only update their database periodically. I read something about this a couple of years ago.
Search engines are constantly updating there databases. It's not like a weekly thing, its more like it just continues to cycle through one site after the other. Since there are many sites it can take a while for a search engine to get back round to crawling a site with a link to you on it. But once it does, it makes changes to your ranking immediately. Eventualy it will have found all your new links and you will see the full effect of them** **not actually full effect, a link will be of more importance to your ranking the longer it stays in place. I usually find that I can see significant movements within a week or 2 (for uncompetitive niches) - to see the full effct of those links usually takes 3 to 6 months.