It allows them to research a wide variety of topics at the click of a button, instead of digging through books, newspapers, and/or magazines. Everything is there waiting for you.
Unfortunately, a lot of the material found on the internet is not credible, but most students do not know how or care to learn how to decipher what is valuable and what is not. Anyone can write their opinions and place it online, that doesn't make it factual or beneficial. Most students just use what they find rather than evaluating the sources. This just hinders their learning.
Students become too dependent on the internet for research and, consequently, have no idea how to find relevant information from a book source. They don't understand the basic principals of the Dewey Decimal System, which just seems like basic knowledge to me.
Also, the internet is very tempting. Students may go to the library to use the internet for research, but end up checking their email or breaking through to their myspace accounts. They easily get side-tracked because everything is right there at their fingers.