I have an old project that I dusted off today that uses the Omni frameworks. It’s old enough that I remember a time when the frameworks built without a hitch.
Then they stopped building. I searched on the Omni Mailing Lists page and found a variety of build problems people were having.
But the message I needed to read was this one, which says “Even if you’re building with Xcode, you may want to stick to the .pbproj projects….” Turns out the *.xcode files are outdated, despite the fact that it’s a newer project file suffix. With the *.pbproj files, everything builds fine.
Should it have occurred to me to try the older files? Sure. But a Readme note, or removal of the outdated project files, or some update in the six months since this was last released, beyond an obscure mailing list message….would’ve saved me some trouble.
Weaponized Fluff 
I completely agree with this – I ran into the same thing months ago, as I’m sure did many others.
It would be nice if someone at Omni included this information, but I hesitate to fault them since they give the whole framework out for free. I’d rather have the undocumented framework than nothing.
What is needed is a central, unofficial repository of information regarding the framework, including examples using their objects and paradigms. To some extent, this has been done:
http://www.cocoadev.com/index.pl?OmniFrameworksDocumentationProject
…but I’d like to see it expanded, or at least given a more visible face.
(Yep, a suggestion but no action. 🙂