Self taught but I think i can foster bad habits and long ways round of doing simple things that just become a habit when you don't know better.

I made a lot of leaps and bounds when I was doing some adaptations of designs for different formats; a really expert designer had put together a master and I had to make it fit lots of odd shaped things, getting to see all of his work as bare illustrator/photoshop files really helped me "get" proper use of layers, various effects etc, I guess online tutorials are similar and have occasionally referred to them when I wanted to do something specific but wasn't sure how to.

But then, that's just software, I learned design before computers were such a common tool with pens, pencils, cutouts, montages etc., looking at other people's work and figuring out how they acheived certain things, I agree you shouldn't copy but you should look at other's work for inspirations and ideas you can do different things with.