La importancia que tengan, depende de tus necesidades y a donde orientas tu web.
De todas formas en la page oficial tienes una explicacion perfecta. (Hay que buscar antes de preguntar)
Código Botones:
Ver originalGoogle PR
Google PageRank of current page
Google Index
Number of indexed pages. Google version.
Google link
Number of links, pointing to the current page. Google version (Except links from concerned domain).
Google cachedate
Date of current Google cache.
Yahoo Index
Number of indexed pages. Yahoo version.
Yahoo link
Number of links, pointing to the current page. Yahoo version (Except links from concerned domain).
Yahoo Linkdomain (LD)
Number of links, pointing to the current domain. Linkdomain (LD) operator finds pages linking to domain, as opposed to link which finds references to a single page. Yahoo version.
Yahoo Linkdomain2 (LD2)
Number of links, pointing to the current domain (2-level domain). Linkdomain2 (LD2) operator finds pages linking to an entire domain, as opposed to linkdomain (LD) which finds references to a current domain (subdomain for example). Yahoo version.
Yahoo Directory
Domain presence in the Yahoo Directory.
MSN Index
Number of indexed pages . MSN version.
MSN link
Number of links, pointing to the current page. MSN version (Except links from concerned domain).
MSN Linkdomain (LD)
Number of links, pointed to the current domain. Linkdomain (LD) operator finds pages linking to domain, as opposed to link which finds references to a single page. MSN version.
MSN Linkdomain2 (LD2)
Number of links, pointing to the current domain (2-level domain). Linkdomain2 (LD2) operator finds pages linking to an entire domain, as opposed to linkdomain (LD) which finds references to a current domain (subdomain for example). MSN version.
Yandex CY
Yandex Rank of current page.
Yandex index (russian SE)
Number of indexed pages. Yandex version.
Yandex link
Number of links, pointing to the current page. Yandex version.
Yandex catalogue
Domain presence in the Yandex Directory.
Rambler index (russian SE)
Number of indexed pages. Rambler version.
Rambler top100
Domain presence in the Rambler top100 catalogue.
DMOZ Directory
Domain presence in the Dmoz Directory.
Alexa Rank
Traffic estimation index
WebArchive age
First date in Archive.org
Del.icio.us index
Link to del.icio.us history for current url.
Technorati index
Link to Technorati history for current url.
Digg index
Link to Digg history for current url.
IP lookup
Current domain IP.
Whois link
Link to the Whois record of current domain.
View source
Link to the source code of current web page.
Check robots.txt
Check if robots.txt file exists and if it does show link to it.
Page links
Dispaly quantity of internal/external links with the link to the link list.
Baidu index
Number of indexed pages. Baidu version.
Baidu link
Number of links, pointing to the current page. Baidu version.
Wikipedia (EN)
Number of search results found in Wikipedia (EN)
Ask index
Number of indexed pages. Ask version.
Bloglines
Number of search results found in Bloglines