Unlike most people, I am all for adding skills into the game. Note I said skills, not skilltrees. Now, back to the topic. I love the idea of skill degredation, and it makes your character feel more like a real person. But maybe instead of the skills showing up in a new tab, maybe have it shown through a characters actions. Here's an example. Lets say you need to cook up some food. This also goes a bit into crafting, but we're focusing on the skills. You have the food required to make a dish, but your character never cooked anything before. So it might take longer for them to cook, or the end result would end up being burnt or undesirable. But through that experience, they gain a little bit more knowledge, and as they continue to cook, or even read books on cooking more and more, they get progressivly better at it, and you would see it through their actions. Now for skills on actually finding the said foods or materials, that would be handled by player skills. Players skills are pretty explanitory. Can you shoot well in other games? Yes? Then you can shoot well here. Can you drive well in other games? No? Then prepare to crash, over and over and over etc etc. For gathering materials, you can learn about the necessary components from books, like what an item looks like, what it's used in, and where you can usually find it. Even if you the player don't have this knowledge, you can still look for and pick up the items like you would anything else in the world. As for the rest, I like the concept of loosing skills if you forget them, or you don't have a certain book to help you, or you forgot to jot down notes and the like. But to add to this. If you die, you lose EVERYTHING. All of your skills, items, everything, GONE! You'll have to start all, over, again.