tl;dr: The further "consolization" of PCs into the forms of tablets and smartphones, and subsequent shrinking (not death!) of the PC market.
The accessibility and ubiquity of smartphones and tablets means that many people who did not or would not otherwise use PCs, often the young and old, frequently use these. To be honest, most people really don't need complicated, vulnerable, expensive PCs. (I suppose most people on this forum are not 'most people' at large.) Locked down tablets and smartphones can solve all three of those problems... for better or worse.
The most serious deficiency of tablets and smartphones in my opinion is input, and we're seeing the beginning of this being solved with optional keyboards, with things like the Eee Transformer, Zagg iPad keyboard case, and the Motorola Atrix.
This would be my best prediction as to the direction things are going to go. People who don't need computers for anything beyond facebook and 'Apps' and the occasional word processing... having all those basic features on smartphones and tablets that have GOOD input options and the ability to print means PCs aren't needed. I can see the laptop and inexpensive desktop market being further hurt (not killed) by this. Once people realise they really don't need PCs, they'll stop buying them. This is why the PC gaming market has shrunk so heavily. If all you need the PC for is games, then a console starts to look like a good idea. The same could be said for net connection and facebooking and whatever other silly things kids these days are into.
Edit: I guess this isn't really a fad... I'm bad with fads