I just read this post on Zak S' blog (which is very much NSFW, even if only for the name).
Edit: As I understood it, he's challenging people to compare which one is cheaper and more satisfying to the group-preparing to run a module, or preparing the session by themselves. Then he invites them to post the results.
Now, Zak called me after this post was published, and explained he meant nothing of the sort. He merely invites people to do both and compare the experiences, not to look for the "superior way"! Therefore, it was my misunderstanding that sparked the following post.
Even so - I still think it's worth trying both. Especially if you're using modules, I invite you to participate in said experiment.
(Personally, I'm sorry, but I simply can't join. I need more time to prepare a game from a module! Yes, tried that long ago, the difference is about 300% more time when using a module. Therefore, I couldn't compare the two, as one would be in unequal position. If I was to use the same time I use weekly in order to preparing for running a session from a module, I wouldn't get to run the module for about 4 weeks!)
Really, guys (and gals, and whatever other word you might like being called) - screw modules!
No, wait, that's a fate too good for them. Rather, forget modules!
You can do better by yourself. You really can. And it's going to feel a lot more entertaining, because it would be tailored to your specific group.
Does it mean I see no value whatsoever in modules? That would be wrong.
Modules can be used as a short-hand way to showcase a setting. You can use them to show typical NPCs, typical conflicts and themes in a setting. So, I like having one, max 2 modules, as addition to the setting's book (provided they aren't some railroad schemes - I learn nothing out of those).
And of course, I don't mind them provided they aren't taking too much space. In Fates Worse Than Death, the book itself has 2 modules, and I don't mind. But the book itself has a great setting, and it's 485 pages setting+system combined! If the book had less than 200 pages? I would have minded even 1 module.
In short, there are some uses for a module. But making running your games dependent on having/purchasing a module? Come on, people, you can do better than that!