I like subdomains. I think it's cool to have sites with URLs like mycar.debayo.com or myhouse.debayo.com and something like that.

What I don't understand is why Google treats subdomains as separate sites. I mean, if traffic goes up in mycar.debayo.com this does not affect the SEO of debayo.com. Why is that? Are they indeed separate sites with different IP addresses?

It used to be that subdomains were looked at to be different sites, however that's not the case any more these days. These days they're considered PART of the main domain name.

The information you have posted was correct in 2009 and years prior, but these days it's no longer the case.

How the "subdomain" is treated is really up to you. You could easily have your DNS server resolve any "subdomain" to the same IP address of the core domain, or you could set subdomains to resolve to different IP addresses.

The "sub" part of the subdomain is just a host header. The domain is supposed to be the actual host. You can serve different sites using subdomains by setting up different sites in your web server (apache/ IIS, etc).

I am assuming you are speaking of Google's Webmast Tools ...

When you initially set up the site(s) using Google's Webmaster Tools, you actually have the option to treat all subdomains as part of the same domain, if you wanted it to work that way. Take a deeper look at the Google Webmaster Tools, Go into the main site (www.site.com), go to site configuration -> settings. Look under Preferred domain.

Here is Google's help link

http://www.google.com/support/webmas...er=44231&hl=en

Hope this helps answer your question.

subdomain is only a part of SEO, unless you got a big amount of traffic, it has little contribution to your main site.

Well as your 2nd level name is not registered TLD or CCTLD, it will be always considered as sub domain. Because subdomain used DNS zone to point to server instead of nameserver record.

As you know,subdomain can be treated as totally separate domain,be pointed to a dedicated ip or binded with separate directory .

Subdomain can be a totally separate domain than the main because it powers you to point to a different server and usually it is used to represent a separate department in your business but yet it is treated as a part by search engines.

It depends on your server and DNS configuration

I would say just completely forget about the matter of PR because although your new subdomains might get promoted and gaining top ranks within a short time via using links plus contents, but their PR might not move a bit.

Besides, Most experts nowadays believe that PR is only one single factor considered by Google and if your homepage has very low PR but getting links from trusted sources, its ranks would get improved soon.

Registration of a new domain is too affordable these days and why getting worried about ifs and doubts of having subdomains when your new sites could be up and active in no time?

Subdomains if could be given a seperate panel, then they can get a dedicated IP.

Yes, sub domains can be used as a regular domain. According to your hosting provider they will escalate whether or not you can buy a dedicated ip with a sub domain. I do not recommend using a sub domain for a domain with an ip, but you can do it.

You can make an A record in you DNS-settings that will forward to the ip that you gave.

Sub-domain can be treated as a separate website. But Google will still show all your sub domains (whether relavant to the main website or not) when you search for your domain.

Yes,
The Subdomains (subwebs) on a subdirectory have their own IP address, and they are aliased to the directory using the IP.
Subdomains may have their own email accounts too.

This is no longer the practice nowadays....