Is yahoo against agressive linking now?

IMHO it has nothing to do with Keyword density, but age may play a part. As stated on another thread. I have two new sites that when they were first created, I placed a few links to them to help get spidered.

To my surprise a few days later they were both ranked very well in yahoo for their primary 3 word key phrase. About a week later I added a lot of links to both sites and the following day these sites were gone from Yahoo for all the links and anchor text phrases I pointed at them.

IMHO this could be some type of sandbox that filters a site if to many BLs are added at once. I do believe that age is a factor in the calculation for what is considered to many BLs at once. I justify this with adding a good bit of links to an older site and it hasnt moved from its present position.

Yahoo is playing with its index, just the other day for Las Vegas real estate, yahoo had over 18 million pages showing in its index, where it has been 5 or 6 million.