A better question would be how much will the rumored 7 inch tablet change the equation? Without the tablet in question, my bet is that between the Nexus series, the new Nooks and the new KIndle Fire series, Android will close the gap and capture the remaining non-iTunes customers out there in the seven inch market segment. They will not convert current Apple customers who are already invested in the Apple ecosystem.
On the other hand, I don't think Apple will gain much new business (outside their current customer base) with their new tablet. I suspect that most of the sales will be to customers who already own an iPad and are looking for a more portable and/or cheaper version.
Given all the Apple rhetoric about fragmentation in Android, it will be interesting to see how they pull off a smaller tablet without scaling some of the interface and creating...more fragmentation in IOS.
Last, savvy customers will look at these new choices and their respective ecosystems and weigh the portability of the ecosystems, meaning either get looked-in to iTunes without much possibility of freeing that media library should they leave vs. Google, Amazon and a host of other venues to acquire media through. A lot will depend on presentation of those choices.