Great question. I think it's ok to deep-dive in (as long as you wade in). I know some friends who have always worked for themselves, and I am always impressed at their constant confidence. I observe some older folks (and even some around my age) at work and I see they're going through the motions sometimes - I don't want to be them. Build something with passion..
I'm starting to learn Ruby/Ruby on Rails on my train commute. I'm doing this to broaden my skill set (specialize in Java for my job). It's slow going at times and sometimes I only do 15 minutes a day.
A major project at work has (almost) come to an end (1.0). And I'm worried about the inevitable screeching-to-a-halt (from overtime busy to idle bored). As a result, a few of us at work are thinking of pitching a Ruby on Rails project to key decision makers (it would be perfect for the application in mind). I'm almost convinced I'll need to build the prototype on weekends (but once we have it - it will sell itself - and they'll give us the go ahead). And the best thing is when we successfully sell the prototype, I'll be able to officially use Ruby on Rails on company time..
Of course, I have a small laundry list of projects involving web mashups/integrations that I want to implement (with RoR).
Like procrastitron stated, all of them are projects I would use and if other people liked them (side benefit). I had trouble with pointers ten years ago so Objective-C is probably a stretch - I'll throw this iPhone application idea out there - I got a seeming mass text from a friend 'Hey how are you. What are you up to' - iPhone app idea: Group broadcast SMS "mail merge" - Hey . I haven't talked to you in What's new?'
If I had a long-term plan... it's trying to diversify my technological skill set. And, I'm constantly trying to diversify my overall portfolio with long-term side projects like Salsa dancing and public speaking (with the aim of getting out of technology [maybe]). I find I learn (about startups, business, and the business of technology) by osmosis just by reading news.YC. I love the news.YC community (8aweek keeps it from being an obsession but I cheat on the weekends).