The most important step in overcoming writer’s block, then, may be cutting it down to size: grasping that it’s just a situation, not an underlying condition, and that it’s solved, by definition, the moment you write anything. You could keep a dream journal, as Graham Greene did, or do “morning pages”: three pages of whatever comes to mind first thing. Give up writing in binges, and focus on doing a tiny amount, very regularly, including stopping when time’s up. Oh, and stop expecting writing itself to be pleasurable. (I’m deeply suspicious of anyone who claims it’s fun.)
Suspect me, then! I like writing; I think it's a blast. I also think it's hard freakin' work. The two are not mutually exclusive. Many people I know, myself included, are at their most engaged and "present" when they are working on an intractably difficult problem.
To the point: I don't get writer's block very much. That is, when I have a project I'm working on, I tend to be able to work on it relatively smoothly, barring any real-life interruptions. The few times I do get blocked, it has mainly to do with one of several incarnations of the fear of failure. It's not that I can't think of anything to write; it's that I'm worried what I do think of will simply have to be discarded because it'll turn out I'll come up with something better, so why bother?
The kinds of exercises described above are aimed at loosening that sort of self-stricture. It's of a piece with what Peter Elbow made the center of Writing Without Teachers: by making writing a habitual, almost thoughtless process, you remove or at least reduce the sense that any effort could be wasted effort. It's all adding up and going somewhere. If all you can think about is a finished product sitting on someone's shelf, then you're going to be that much less able to see yourself as invested in the process rather than the product.
I think the reason this type of unguided writing has been given a bad rap is because people see it as an excuse for mere logorrhea, and as a justification for passing off that kind of stuff as profundity. Unblocking the channel isn't by itself the problem; it's whether a useful process becomes developed from that or not. Elbow wasn't just talking to people aspiring to write fiction, but people who wanted to write, period, and those people suffer no less, sometimes even more so, from blocks and anxieties about seeing their work as an artifact rather than a process.
Artists who deal with other media always have interesting things to say about what they do is a process. I think that's one of the reasons I got curious about how actors are trained, for instance. You can film a performance or record it, but in the end, the performance, the process itself, is all you have. It's the same with all the arts, but it's more explicit with some and less explicit with others. Another reason I keep thinking there's as much to be learned from a painter or a musician as there is from another writer.
Want to see what kind of writing I do when I'm not blocked? Check out my (new!) novel Welcome To The Fold, and showing your support for it by registering at Inkshares and adding the book to your "Follow" list! Failing that, you can always buy one of my existing books, available on Amazon Kindle and in dead-tree format.