I got rid of my mac mini because I tend to not take my MBP 15" anywhere because of my ipad. So I put the MBP in the place of the mac mini. Didnt really need all three. Take ipad everywhere.
My ipad has not really affected my use of my laptop: I tend to use the laptop much more because it is so much easier to type. I use the ipad for reading, video and web browsing, mostly lying down on a sofa or bed.
I have a Macbook Air 11", and honestly, it's easier to use and type on plopped in my lap in my recliner than it is to hold and use my full-size iPad 3. And for me and the kind of work that I do, there are still a lot of things I can do much easier on the Air that are harder or impossible to do on the iPad. I like the iPad for reading books/magazines, viewing photos, news and weather apps, and of course on-the-go use.
FYI - I'm a public school teacher, and content creation for my classes using Keynote and Pages is still easier on the Mac than on the iPad, as is video editing using iMovie, MPEG Streamclip, and other Mac apps.
Oh boy! You'd be shocked by what my kids have put their iPads through. My youngest has been caught accidentally jumping on his. The iPads go everywhere with us. They are in cases that protect the iPads but I don't really stress about them. My oldest uses his a lot for reading, researching, watching videos etc... And his is fine after 2 years. We haven't had problems with any of our 7 iPads that we have owned. I'm sure ours have been through more wear and rear than 90% of the iPads out there. My brother just bought my youngest's ipad 2 since I got him a mini and there was one tiny scratch on one corner and that was it.