Just out of curiosity, and because it's always fun to resurrect a dead threat, but what do you do about mashups?
I know that today, the Beastie Boys could never release Pauls Boutique, due to new restrictions on sampling. However, in modding for TES games, it seems to be fairly common to take a mesh from here, a texture from there, etc.
I'm working on what I believe to be a fairly unique mod, and I find I need fairly unique meshes. I haven't mastered Blender, so I use nifskope and bits and pieces from other meshes and textures.
http://img218.imageshack.us/i/ravenwood332.jpg/
This sewing machine, for example, is pieced together from bits of two different mods, and a pipe from stock Morrowind that I manipulated to act as the arm for those thread spools. I can't quite remember where the original machine came from, but it was clearly a mash-up of stock bits and something else (gods only know from where). The table was a third-party Oblivion model that I downgraded. I keep a copy of the original archives on an external hard disk so I can pull the credit information, but in some cases, a single model might have multiple credits.
http://img269.imageshack.us/i/ravenwood189.jpg/
This is another mash-up I did to create a computer terminal. Care to guess how many meshes I pulled pieces from? I'll give a hint - it was more than 5.
Also, to maintain a fairly consistent landscape, I've completely redone every tree, rock, or water mod I have used. In some cases, I had to alter/correct collision data. In others, I needed to fix texture problems with the UV map. All of the terrain models have gotten new textures - most of which came from replacers. Same with furniture. I've had to redo practically every piece I've downloaded with new UV maps and textures. In some cases, I've actually had to fix the piece. Then, there is the retexturing to maintain continuity. (For example, my jail has very 'bureaucratic' wood grain furniture, even though the individual pieces came from different mods or stock meshes, to make it looks similar to the station in Hill Street Blues)
Practically every model I'm using has been altered in some meaningful way, and there are a lot of them. I haven't done a count so far, but I'm looking at hundreds of these altered meshes in the final mod.
Then, there is the scripting. I wanted to add ASE support to my mod, but it quickly became apparent that it was going to be a disaster. First off, ASE assumes that your interiors are interiors, not interiors acting like exteriors. So, I figured out, more or less, how the thing worked, and recreated it for my mod. I nuked almost all of the original code in the process of stomping mod-specific bugs. About all that is left of the original mod, other than the concept, and the code for handling lightning effects, are the sound files.
The plan right now, since I have a lot of models that are mashups, or are heavily altered, is to credit the modders whose work I used period. I will break it out for some mods that are used almost in their entirety, like Barabus' clocks and fireplaces, or Kat's gowns (which she gave me permission to use at my request) Otherwise, I'll have to write a novel after I finish the mod explaining the relationship between models and modders. I have restricted myself to mods that allow such usage, or gotten specific permission, but at a certain point; specific credits are going to be darn well impossible.
Then, to top it off, just because a resource pack says you can freely use it, doesn't mean you can. I'd have to look, because the resolution is kind of low, but some of the images from a previously linked site look eerily similar to images in one of the texture packs I'm using... Sheesh!