Well, I can tell you what worked for me. I don't get along too well with formal education, either (including seminars), so this may be of some relevance to you. Or maybe not.
First, credentials: I've been a professional software engineer for almost 15 years now. I've played a major role in several well-known products for MS-DOS and MS Windows, such as Norton Utilities, Norton Anti-Virus (early '90s) and the After Dark screen saver (version 3.0 for Windows, the first one that really worked right). I'm currently with a network management company in Silicon Valley which went from being a startup in '96 to being acquired for a nice chunk of change last year. Technology I conceived and implemented almost entirely by myself played a central role in the success of our products.
Despite all this, I have no college degree whatsoever, although I (perhaps arrogantly) feel that my technical skills and theoretical knowledge of computer science and software engineering are as good as that of anyone I've ever worked with. (Or perhaps not so arrogantly -- my manager, a very capable technical fellow himself, recently said much the same of me.)
So, how did I get this way without a proper university education?
What I've always tended to do is, more or less at random, become curious about some aspect of programming or CS (they are not the same thing) that I have never previously explored in detail. This aspect might be "how networks work", or "functional programming" (my most recent obsession), or some unfamiliar language (I'm a definite language junkie, though I'm getting more selective as I get older). I then look for authoritative sources of information about it, such as a well-regarded book or a web site full of relevant papers and tutorials. I download any freely-available tools that may be of use (compilers, for example). I come up with interesting little projects to do to get first-hand experience. I join a newsgroup or a mailing list (preferably the latter) and participate in it by asking hopefully-intelligent questions and trying to answer other newbies' questions when I think I can. (This occasionally leads to "no, that's wrong" replies from people who know better, but that's all to the good.) I debate theory with experts in these forums, too, once I think I have half a clue about it. Most importantly, I try to understand fully both the theoretical background and the practical issues. And I always remain model-agnostic; learning a new paradigm only to treat it like the Holy Grail is merely the path to mindless fanaticism, not true understanding.
I feel like this may sound too pompous and self-satisfied, for which I apologize; the error is in my expressive abilities, not my judgment of myself, I think. I know I don't know everything, or have perfect judgment. That said, I think I've demonstrated, in my career, that I'm a very good engineer, and the above is the best quick summary I can manage at the moment of what I think has been most crucial in my becoming one.