This is an interesting question and one I've been pondering lately as well, not from an individual perspective, but from a management perspective for a small team of developers at a web app/design shop.
I obviously have to be more conservative than you because I have to consider short-term profit as well as risk. So in order to get responses that are along the lines of your question, I'd like to ask HN readers: what do you think is worth concentrating on in 2010 that would lead to good short- and long-term results for an agency specializing in website and web application development, often for relatively small projects?
To answer your question, I think you need to do some thinking about what it is that you want to do. You have to start with something that interests you. Your friends chose something in the realm of mobile development: does that appeal to you? Perhaps they also focused on games: does game programming appeal to you? Someone below suggested "data mining" as a field to focus on. I can say for myself that although I am somewhat interested in this, I am not anywhere close to as interested as I'd need to be to devote several years to it.
It also has to be something with a good chance of paying off, if you are interested in the money side of it. Your friends chose something that was backed by a huge corporation with a proven track record of creating successful devices, so although they ran some risk - the iPhone may not have been a massive hit like it was - they mitigated that risk by choosing something with very good chances. However, any choice that relies on predicting what will be successful in the technological realm in two to three years is bound to be risky, especially if it is "very new" (and thus unproven).
Here's a shot at it: focus on mobile web application development utilizing HTML5 features. Google believes "the web has won", and I agree. If you get really good at building browser-based applications for mobile phones, I think you'll do well.