I think the question is really not if new devices likie tablets will bring the PC market down. That's difficult to imagine at least for the short to medium term. Lots of stuff just can't be done on something else than a PC type of computer, and I think that will remain the situation for quite some time, but it has transformed the PC market to a mature or maybe even stagnating market. Another question though is if smartphone ecosystem(s) will continue to completely dominate the tablet space. I think Windows based and Linux based PC-type of tablet devices do have some chances to carve out a reasonable niche, especially in corporate and embedded applications i.e. non-consumer markets.