Lead data transfer from Pardot to Marketo

Sorry, you can't migrate that data. The closest thing is to migrate Program Membership. For example, someone clicked on an email in Campaign ABC in Pardot. To migrate, create a Program in Marketo called "Campaign ABC" (channel: Email Blast) and import the list of people who clicked into the Program as members with a status of "Clicked". 

Ditto for me.

Gary - Jep is right. You could also create Lists like 'Tradeshow 2012 Attendee' etc, and import list of attendees into that particular list into Marketo. Alternatively, if you'd like to maintain history of how engaged someone ever was on your website/content, you could import their Lead Scores from Pardot into Marketo. That way you're not completely not having visibility into people's levels of activities. The Lead Score can serve as a good indicator of how engaged they were, or their fit score. 

Building upon Gary W's question, is there a way to stamp their history retroactively in the manner you explained above? (i.e. if you wanted to stamp Prospects with registering for a webinar on March 4, 2009, would you be able to set the date for the activity when importing the list of prospects from Pardot and have it appear as though they completed the activity in the past?)

You can't change the dates in the Activity Log, but if you create programs for past campaigns, you can set the success date to a past date for groups of leads that came by your booth, attended a webinar, etc.  It's a bit more sophisticated than just creating Lists as Kashmira suggested, but a lot more work.

I think there may be a potential workaround. Pardot has a help page for exporting prospects that notes

"we are unable to export a prospect’s full activity history. However, if this is information you are looking for, you can query the API in order to retrieve it."

http://www.pardot.com/faqs/prospects/exporting-prospects/

Specifically, I'm looking at visitor activity such as search phrases and page view URLs, which are listed in the API documentation:

http://developer.pardot.com/kb/api-version-3/object-field-references#visit

The issue here might be developer time on our end to jump through all the hoops.

Even though you may be able to get it out of Pardot through the API, there is no way to get it into Marketo Activity log. You can only import into Lead fields, or you can set Interesting Moments. 

I can imagine you may want "original search term", and you can save that in a Lead field. However, why would you want to know which pages someone visited in the past? That information is most valuable going forward. 

Yes, sorry if I wasn't clear--I was presuming this would be an import to a lead field. The URLs that have been visited previously on our site include categories that allow me to funnel leads into specific content channels (e.g., if someone visits a page that has /Microsoft/ in the URL, I can send them content related to Microsoft).

I'd like to have that historical activity from Pardot in a custom lead field, then create a smart list filter to search "Previous URL contains TOPIC" to add them to a particular content drip.

If you absolutely want to do it, you can use the "Interesting Moment" feature to populate the values over SOAP.  I would not recommend adding the entire pardot history this way, but only select activities that would qualify as "Interesting Moments".