I've always been a skimmer. With most writing, a good portion of the words can be skipped without missing much content. The web hasn't changed this for me. I did it before with print books including fiction for entertainment.
Sometime when the subject matter is deep or densely packed I have to make myself slow down. Usually this isn't the case though.
I read a lot of fiction... (checks kindle) looks like about 100 books a year. I definitely start skimming when the story isn't engaging enough.
Roughly speaking, I think the better a book is, the less I tend to skim. A truly great novel I will read at probably 10% of the speed of a bad one. (If it's really bad, of course, I stop reading and throw it away.. that's probably the case with 20% of the novels I start).
With most nonfiction, technical books, etc., it is different -- I skim as much as I can while still extracting the info/knowledge I am trying to get out of it.
Depends on the book but I've definitely found some dense technical books (mostly textbooks) have to be read much slower than my normal speed for real comprehension.
Sometime when the subject matter is deep or densely packed I have to make myself slow down. Usually this isn't the case though.