I think the SP3 has done a good job replacing my laptop (would like a slightly bigger screen) but has not replaced the iPad. This has nothing to do with the device itself (which is great) but everything to do with the lack of Metro Apps available.
I know many of you disagree and say that you can just use the browser to access HBO Go, NHL GameCenter Live, Banking, and other sites, but those apps on the iPad are much more convenient from a touch prospective.
So no, due to the lack of Metro Apps, I don't think the SP3 can be a complete iPad replacement.
This has been my experience. While i use the surface almost exclusively, i still don't have any plans to give up my nexus 7/10 for those rare occasions where i have a use for them simply because of it being easier to use. Banking being a good example. On my surface i'd need to have my card reader, remember a long pass code etc. On my tablet i touch one icon, enter 6 numbers, and i have instant access to all of my finances.
I've also started using my nexus 7 a bit more in bed. It's a bit more girlfriend friendly. A new approach to the argument 'size matters'