Google's recent Jagger update (October 2005) was notable for the number of sites that just dropped off the face of Google entirely. Some of them were highly ranked, and I know of a couple that had held the #1 spot for their keywords for eons. Yes, Jagger certainly ruffled a few feathers. Can't say I'm sorry though: the sites that I saw disappear were definitely the "spammy" type.
So what have we learned? The algorithm experts are still trying to come up with concrete answers, but we do have some firmish information to work with.
The Purpose of Jagger
Jagger, it seems, was at least partly designed to weed out websites that were guilty of participating in paid linking schemes. We're not talking about link farms here, but the kind of schemes that would render respectable links for a price. They're no longer ethical.
There are two ways of looking at this.
Good or a Bad Think?
Google has every right to try and filter websites so that searchers get exactly the results they're looking for in the form of quality sites. But on the other hand, if search engines are going to accept paid listings, then why penalize someone who is just trying to get ahead through a different channel, with no ostensible difference to the final results.
Personally, while I acknowledge the need to ensure that only quality sites get to the top of a search, I still think that it's essential not to restrict webmasters too much when it comes to what they can do to get noticed.
Having said this, it makes sense to heed warnings if you're serious about getting a good Google page rank. Paid linking strategies are now out. Be extra careful about who you link to.
There are some rumblings that Google will ultimately reduce the importance of links when according page rank. This does make sense in my humble opinion.
Basically, we'll all have to wait another few weeks to see exactly where it's all going.
Oh, one more thing. If your site was one of those that suffered at the hands of Jagger, remove all hidden text or hidden links and read Matt Cutts's
information on a request for reinclusion. Good stuff as usual.