Will also add I haven't had too much problems with downloaded object. There are some free stuff that the user just breaks packing it up, and there is a website that repacks downloads, so you gotta usually extract the texture separate to the object folder. But most people I've downloaded good quality objects from pack up what the program exports, which is usually always relative paths. I haven't really ever countered a full path from someone elses PC in downloaded objects, actually that's mostly a Terragen project issue.
It would be cool if Terragen just started every project like a gathered project, and require a folder to save too, making everything relative for use across platform, render farms, and general project management. Every image and object you load into a project, is copied to it's asset folder.