The latest Final Cut screencasts cover adding a simple lower thirds to your project and creating a lower thirds template for use in multiple projects. If you know of a better way to create a lower thirds template within Final Cut (not using Motion or LiveType) please let me know. I managed to find a way to create one from my own experimenting and am not sure if it is the best way to do so.
When viewing in full screen I would recommend watching in HD in order to make out the text.
Good idea about the exporting xml. I never knew you could do that with the text features. As far as making fancier lower thirds I always just create them in Photoshop and bring them into the project. FCP will even import psd files so you can use layers to your advantage for dynamic lower thirds.