I recently read my first book online. It was an online text version of The House Behind the Cedars for my english 301 class (Intro to Lit for English Majors). I can honestly say that while I saved about 8 bucks reading it online I much perfer having a paper copy of books. Reading an entire novel online is a strain on the eyes.
anyway...onto the next part of what I wanted to say;
Most teachers both in High School and College level classes ask for book, magazine or journal sources in addition to the web sources. They'll put a minimum on the number of non-web sources. Checking your web sources for credibility should be brought up in research type classes, I know I've had a couple instructors discuss this issue.
Nowadays many print sources can be found online. I know my university has a library webpage where many journals can be accessed online in full text (some only students can access).
http://www.lib.umd.edu/ I used this for an anthropology assignment and it worked out quite nicely. I think that its great that many books, journals and otherwise generally printed material can be found online now. This feature makes accessiblity a lot better. Most libraries do not have it all. Tho, neither does the internet which is an important thing to stress.
I dont think print sources are becoming obsolete, I just think that people are turning to them less for "basic" information or quick lookups. I love books, thus my major, and I hope to have a rather large bookshelf/personal library one day. I think thats where almost all my spending money goes. I must admit tho that I frequently use the web for information and libraries often frustrate me (esp. when they are reorganizing stacks or something of that nature which makes things exceedingly hard to locate). My guess is a lot of people feel similarly.