I did something today that I haven't tried yet. I decided to stand in Balimund's forge in Riften with my healing spell at the ready to get my Restoration skill up. Everything was going as planned, when I went up an actual level and was about to move on my Destruction skill randomly increased a point. When you take on fire and ice damage of any kind does this increase your Destruction? I've never seen this before and I've been playing this game for a while, but like I said I've never tried this before and/or paid attention while getting attacked with destruction spells because, hey, I'm usually focused on not dying at that point ;)