Is the explosion in demand for User Experience experts a trend or a bubble?
It's definitely a trend but it CAN become a bubble. I'll explain.
Over the past five years I've seen UX go from an isolated discipline to a field where UX talent is in high-demand. The primary reason this happened is because applying UX processes has shown to be successful. Researching and understanding customer needs and then creating useful and usable solutions that respond to these needs (that are also desirable by said customers) has worked.
When decision makers at companies see something is working in other companies, many of them decide they want "some of that." Some companies are more serious about integrating UX into their processes than others, but all who "try out" UX provide another opportunity for a successful case study that keeps the "ball rolling."
Where UX can be a bubble is if UX becomes too homogenized and too academic. When I say "homogenized" I'm referring to the discipline becoming flooded with what I call "casual" UX professionals. I've seen a lo of former business analysts and copywriters get into the domain and, while many of them are passionate about experience design, quite a few entered the profession in order to, well, continue to stay employed. In this economy that is nothing to criticize, but as the field expands we have to be concerned that many of these casual UX folk bring with them only a surface level understanding and can very easily make all of us look bad.
You may think a good solution to this is professional certifications and training – I disagree, because of my second concern: UX coming off as an academic exercise rather than a vital value-added process for businesses. Too many of my colleagues are steeped in academia, and one said to me the other day "if I had my way I'd be doing ethnographic research forever!" In a booming economy companies can afford more R&D… In the current economy companies are far more budget-conscious and results-focused.
If UX professionals do not focus on providing solutions that meet business needs and understand that they will have to "show ROI" and instead spend most of their time doing "blue sky" exercises… Then that potential bubble?
Ask not for whom the bubble pops, it pops for thee.