Linguistic forms that are associated with younger people and/or the internet tend to be stigmatized because of what I like to call the "WELL BACK IN MY DAY" sort of ideologies that shit on anything new. A lot of discourse about allegedly "bad" and "wrong" language is actually rooted in ideologies that stigmatize certain linguistic forms because of who they're associated with. But it becomes so widely repeated that these linguistic forms are "bad", and even people or organizations that portray themselves as authorities on language are saying that they're "bad", and so it simply becomes a "fact" that they're "bad".
a lot of times i don't capitalize things either, and i'm a linguist. you should do whatever makes you happy. :)
Definitely used books, both because they're cheaper and because I feel like they have more character. Some of my books have notes or indications in them of who their previous owners were.