The Site Analyzer allows you to check the site and link popularity for various domains. The displayed data include the incoming link counts at different search engines, the Google PR and Alexa Rank & Links.
While in "Top Competing Domains List" you can right click and select "Analyze Domain" to add the domain to site analyzer. You can also manually type in the domains.
Right click within the list for more options. You can open the domain related data in an external browser (Alexa data, Search Engine information, etc.).
The lower panel contains the web page structure of the domain highlighted in the top panel.