An excellent thread. At one point I had both - a MBP (2010) and iPad (3rd gen). I ended up selling my iPad within a year. I purchased it primarily for reading/annotating PDFs (academic papers), and whilst good at the task, was too heavy and dimensions too awkward to really be comfortable to use for any extended period of time. By the time I also carted around a smart cover, a case, keyboard etc. (for the occasional writing session), I actually found it all a lot more cumbersome than the MBP. Years later, I must admit that I don't miss that iPad at all - it never found a comfortable place in my workflow. That is, until...
One evening I was visiting my parents, saw my sister's mini 1 on the counter. I picked it up and wow, was I impressed with its form factor. I felt that its size, portability and weight really hit the spot for my usage. The smaller screen was certainly a substantial tradeoff, but well worth it in my case. I 'borrowed' it for a few weeks, and found myself using it significantly more than I had ever used my 3rd gen. I was reading, writing, and doing all the things I had envisaged with the 3rd gen. Since returning the mini (she 'borrowed' it back), I have been seriously flirting with the idea of taking the plunge again. I suspect that I will be amongst the first to own the iPad mini 4 when/if it is released in Sept/Oct. Until then, the MBP will press on in all its glory!
Should I take the plunge, I must admit that I am not sure how i'll reconcile my ongoing issue with all the added bulky paraphernalia (a topic that is rarely canvassed in these threads). Being a cheaper 'mini' device, I may very well elect to boldly go where no self-respecting fanboy has gone before - sans a case). There goes the neighbourhood...