I rarely use my iPhone (except for calling and when I need 3G) since I bought my iPad, and I use my MacBook Pro less. What I do most with my iPad:
watch videos and movies
read iBooks
surf the web
email
take notes with SmartNote
keep a journal with Maxjournal
twitter with ShinyTweet
check my contacts' Flickr photos and make comments with FlickStackr
sync files with Dropbox for iPad
read USA Today, New York Times Editors' Choice, NPR apps
play with Pinball HD, RealRacingHD, Solitaire, and Star Walk apps
check foursquare with Dash Four
create documents with Pages
import and organizes photos from my Nikon D5000 using the Camera Connection Kit
monitor todos with Things app
send SMS with Google Voice
read magazines with Zinio
check the weather with Weather HD and The Weather Channel MAX
dictate notes with Dragon Dictation
read web articles offline with Instapaper
monitor deliveries by FedEx, USPS, and UPS with Deliveries app
read RSS articles with NetNewsWire
sync notes with Evernote
watch YouTube videos
I take my iPad with me everywhere throughout the house and yard (except the shower)
I think I'm getting my money's worth, and I've learned to type quickly with the virtual keyboard, although it took some getting used to.