There were too many PR, marketing, advertising, and SEO bloggers who have asked me what an OPML file is, what they can do with the provided one on the AdAge Power 150, and how they use it.  Well, first, how to use it. Download the OPML from the Power 150 site, and read this, if you read your news on Google Reader like I do:

If you’re switching from another feed reader, you can import your existing subscriptions into Google Reader. To do this, you first have to export your subscriptions in a standard format called OPML. Once you have your OPML file, go back to Google Reader and click the Settings link at the top right, then click Import/Export. Choose the location of your OPML file and click Import; Google Reader will add all the subscriptions in the list to your account and start checking them for updates. (Via Google)

But, what is an OPML file?  Well, that’s easy:

OPML (Outline Processor Markup Language) is an XML format for outlines. Originally developed by Radio UserLand as a native file format for an outliner application, it has since been adopted for other uses, the most common being to exchange lists of web feeds between web feed aggregators. (Via Wikipedia)

If you need to import the OPML into Bloglines:

Once you have registered with Bloglines and replied to the confirmation email, click on the My Feeds tab at the top of the screen. Then, click on the Edit link. At the bottom of the left panel will be a link to import subscriptions. The subscription list must be in OPML format. (Via Bloglines)

And, if you want to import the OPML into Netvibes there is some information you might want to read.

And, if you want to import them (and there are a lot of them) to iGoogle, it is pretty easy as well — but you’ll have to convert it first.

Good luck!