Mine has replaced a laptop for most of my internet surfing/emailing at home. It's great for reading comics as well if you're into that.
I've binned off my CD collection as I can control Spotify from it, likewise no need for a DVD/BluRay collection if you have a media server (such as Plex) that can be controlled from the iPad. Watch a bit of telly in bed via the on-demand services.
Got rid of all my cook books as there's a great app (Paprika) that allows you to download recipes directly from most popular websites.
The number one thing it's great for though (iPad, Android tabs are still lagging a long way behind in this department) is gaming. I just don't have the hours these days to get stuck into "proper" videogames so the tablet fills the niche perfectly. There are tons of games that you can pick up and play for a few minutes at a time. There is a great indie games scene with a lot of innovation, but also now there are big budget titles too. Especially if you like (proper) board games, there are so many excellent conversions on the iPad now.