Just rambling now 
but I personaly think the worst form of SE manipulation is the link exchange.
There was a time when you would find a site of interest and to gather more info you would go to their links page and find maybe 10 sites listed, all of which would have good quality info on the subject matter at hand.
Now when you go to a links page you get a list of a couple of hundred crappy little sites which are there for the sole purpose of improving SE listings – I long for the good old days
Everyone seems to think it’s ok to exchange links for the sole purpose of imroving serps, and many people even use automated links pages and spiders to check that their links are still in place at the other sites. And God forbid if anyone uses a directory script that doesn’t use static links!
There’s other SEO techniques that are used by the so called ‘white hatters’. How about sites that use mod-rewrite to turn dynamic pages into static pages?
This is a form of cloaking that everyone seems to think is fine. There’s no reason why a dynamic page should be cloaked into a static page except that of SEO (and possibly because it looks a bit better, but few people whould make themselves extra work just for this purpose).
Basicaly, what I’m rambling about is that there are many SEO techniques that many people regularly use and think are ok but complain when someone else uses a technique that they don’t personaly approve of (sometimes because they don’t have the skills to implement it).
I would personaly like the SEs to dump every site that engages in pointless link exchanges, although I think ‘dynamic page cloaking’ is fine.
At the end of the day the only people who decide this is the search engines.