Another link to the prolific Shaun McGill, but here he shows how to add extra fonts to Mobipocket Reader on S60 3rd Edition. Pretty cool, I wonder if there's a way to tinker with the main system fonts though? Comments welcome.

"One thing that has aways bugged me about the MobiPocket reader on the E61 is the default font. Just discovered that you can change it. Here’s how-

1. Insert your SD card into an SD card reader and create a new folder called ‘Fonts’ in the Resource folder.
2. Copy some fonts from Windows/Fonts on your PC to this new folder.
3. Re-insert your SD card into the E61 and turn it off and back on.
4. In MobiPocket go to settings/fonts and then choose one of your new fonts from the list. Works really well and brings it close to eReader quality. "