This is a fun and interesting thread. I should preface my remarks by saying that I absolutely need a PC for work, so the context of my comments is personal and home use.
Essentially, I have been using the iPad as my primary computer for a couple of years, and since ios 5, I really haven't touched the family laptop except to do some periodic maintenance and software updates for the laptop. The iPad (and iPhone) has been completely PC free since ios 5. This includes all backups, set-ups, software upgrades, restore from backups...the works. I never connect to itunes.
While I can imagine hypothetical situations that might require a PC, they just never happen for my use case. I primarily use the iPad for:
email
web (e.g. safari plus news, weather, wiki apps)
calendar + reminders
notes
books
finances (Mint & banking apps)
Storing and accessing docs & pdfs (dropbox, goodreader)
photo editing and organization (iphoto, photosync, flickrstack)
video & slideshow creation (imovie)
document creation - usually short Pages docs (iwork)
maps and direction
tracking the kids (find my phone)..sounds lame?...no comments from the peanut gallery unless you have a teenage daughter!

listening to music (pandora, itunes collection)
watch movies & TV shows (Netflix)
occasional games
If your needs are simple (which is often the case for personal use), go ahead and buy the iPad as your primary computer. Give it a go. If you find it doesn't work, you can buy a laptop later when you have better assessed the need and gap (if any) to be filled...perhaps a cheapo laptop will suffice.