The Google Page Rank project is a library and a tool that allow you to query for the Google Page Rank of any public page.
The command line tool can be used to query a page with the following syntax:
googlerank [-r] [-t] '<url>'
The result is output in your console as:
Where the rank is a decimal number. This number may be negative if the rank is either not defined or an error occured while retrieving the information from Google.
The library works well with Qt applications. It offers one class named QGooglePageRank which is used to send a request to Google. The request may take some time so you can connect() to the googlePageRank() signal instead of waiting for the answer. In a Qt environment, this works asynchroneously in a seamless manner.
Detail information can be found in the library reference.
Google limits the number of PR that one IP can check. Over time, if you start having a very large number of pages, this may not work well for you. One solution, though, it to have clients get the PR information and send it over using AJAX. It would not be data from the client, so no problem at that level, but that way we could update pages that end users visit without using our server's own resources and that especially allows many more pages to get a fresh PR.