I've received a number of people interested in this one, so I'm posting it here publicly.

CaseySoftware is in the process of building a complete Microsoft Project to dotProject Importer. This does not work directly with the .mpp file, instead we are working with the XML export.

First, the Importer takes the XML file, creates all the tasks in dotProject. Next, it starts importing Resources by taking the Resource from the XML file and first attempting to match it to a username and then a first name, last name combination in dotProject. Finally, it preserves start/end dates, durations, and dependencies.

Our timeline for release as follows:

Friday, July 8th: Beta of the Importer will be released to all project sponsors for testing and comment.
Friday, July 15th: Comment period ends.
Friday, July 29th: Official Release of the Importer to all sponsors.

We believe that this will solve one of the major hurdles preventing people from moving to dotProject in droves. If you would like to participate in the sponsorship of this effort, please contact me at webmaster [at] caseysoftware [dot] com or join the sponsorship here. Sponsorship starts for as little as $500.

Non-sponsors will have access to the required code approximately 4 months after the Official Release. This will protect the investment and advantage of our sponsors for the duration.