Yes, and I was really hoping that it would do the trick. But it had the following problems:

* I had a choice of 3 input formats to begin with: .img (Garmin specific), .mp (used exclusively by cGPSmapper), and .csv. GPSBabel could not read the first two no matter what I tried. It could read the CSV file, but (as noted in the first post in this thread) that file did not contain "category" fields that I could use in Maemo Mapper. Also, whatever I tried, GPSBabel would not intelligently populate the <desc> or <cmt> tags from the CSV file. Going this route, I got a usable but incomplete set of POIs - name, lat, and lon only, no category, no description.

* Even when I finally massaged the .mp data into .csv format (this took a number of steps), GPSBabel would not populate the <desc> or <sym> tags the way I wanted. I finally had to use a custom script in a programming language called Ruby to format my GPX output properly.

Disclaimer: I know virtually nothing about Ruby, but someone from another forum kindly provided a script that I was able to tweak to my satisfaction.