Positive benefits -
The availability of finding all sorts of excellent information which would otherwise be difficult to get a hold of. For example, I have a family member with a pretty rare medical problem. Pre-online, I used to (would you believe?) sneak into a university medical library and pretend I was a med student, to photocopy journal articles, etc! Once I was online, I was able to find out more information in an afternoon, simply sitting at the computer in the house than by spending hours looking through books of abstracts, and I was also alble to find others with the same problems on forums! And of course, I can do the same for practically every subject under the sun.
Interacting with others across the globe There is little opportunity for me to meet with people from places other than the UK where I live. I only know a very small number of folks from other countries. It gives me great insight to be able to chat with people from other cultures online.
Finding other people with the same interests as me For example, none of my friends in the 'real world' have the same tastes in music as me. The internet allows me to discuss my interests with others who feel the same
The negatives -
I spend more time online than I should - it is replacing too much of the spare time I have which I think would be better spent interacting personally with people in the 'real world'
I would never give up the internet, but it truly is addictive!
Negative interactions - I have witnessed some interactions on forums which have, quite literally, made me feel sick to the stomach, interactions filled with utter hatred. I know they are just words on a screen, but they have certainly affected me. I am all for free speech, but online, moderated forums are my preference.