Is SEO(Search Engine Optimizing) good?
Depends. If you join a webmaster forum, you may notice that some members there, have 30 or more sites about various topics(ringtones, mortages, pharmacy). Those sites contain no good content except some stolen/poor text and affiliate links. Such sites are definitely not good for internet for the simple reason that one person cannot maintain and keep up to date so many sites, so they are just junk, therefore one of the google's goal is to eliminate junk from their search results.
But if you already have a site, and you do SEO just to make it more friendly for spiders, so more people will be able to find your site, then SEO is good. So you should do SEO for your existing sites and not make new sites just to do SEO.
How does google sort search results?
Some say they use pigeons, others say they do it by PR(the famous green bar). But the correct answer is: all internet users that search using google, contribute to the results ranking. How is this possible? Simple, some use google toolbar, others simply help by clicking or not on a search result.
Of course, in order to get into google's attention, a site first needs a few backlinks and some good original content. Then google allows the users to transparently make the ranking.
So how can I get on top of the results?
Make a website thinking to your potential users and what they want to see. Make it SEO friendly but don't exaggerate with this, always put your visitors first. Use ethical promoting methods.
How about PR? Why aren't pages sorted strictly by PR anymore?
Because at some point, many webmasters were using unethical methods to get backlinks, such as link farms, blog spam, aquisition of existing websites with high PR, only for linking purposes (this was bad for the Internet because those sites were no longer developed, they were just abused).
The PR sort was also a little unfair for new sites, which had no change to get on top without getting tons of backlinks. With the new algo, if a site turn out to be useful and used(clicked+browsed), it can get on top positions.
What is sandbox ?
The sandbox applies to new websites, and is a kind of pending status. Google simply says: "Hey you are new, stay down and let the elders first, keep the good work and at some point you'll get into their club too".
This way google can first watch over the new sites to see how often are they updated, how they and where they get their backlinks from. If they get the backlinks at a high rate, they are probably spammers so they will never be ranked good. If their backlinks are up only for a short period, then they probably are buying links or again spam so at some point owners remove the spam or their paid links expire, so the site will be again penalized. Of course google watches to old websites too for such actions, but the elders are always considered more trusted for the simple reason that doorways and unethical sites don't live long.
What is google blacklist or exclusion ?
A site can be manually or automatically excluded from SERPs if it is found to be completely useless for the internet comunity. Such sites usually use spam to get backlinks, they have no content quality but some duplicate or stuffed keywords, and they are full of affiliate links or redirects.
Why META keywords and description are no longer important?
Because they are not seen directly by users, therefore in many cases they were unrelated to the page or outdated. A normal webmaster updates page title and content and often forgets about keywords or description. Meanwhile other webmasters obsessed by SEO, were giving much more attention to META optimization than to content itself. From the user side, the first kind of websites with outdated/missing/unrelated META was usually more useful. So google simply decided to almost ignore META keywords or description.
Is W3C Validation important for SEO?
No, take a look to www.yahoo.com, www.google.com and www.msn.com and you will see that all of them fail the validation tests with several errors. So if they dont care about their own pages, I doubt they care about others'.
Want more? Check http://www-db.stanford.edu/~backrub/google.html