Here is the sort of thing that irritates me. I create a dialog within Mixtikl (using our own internal GUI framework), and run it modally. Within that Dialog, I use Cocoa services to request to be told what Bonjour-advertised services are available. What do I get? Well, nothing, other than a call through the delegate to tell me that searching has started.
It turns out that the processing behind the scenes works only if the active NSRunLoop is allowed to do processing; so I've had to add-in a call like this in my modal loop:
[[NSRunLoop currentRunLoop] limitDateForMode:NSDefaultRunLoopMode];
So you might ask, what is wrong with this? I contend that for such processing, the system should be smarter and use an approach that doesn't require specific magic within the client code (in this case, a worker thread that does the work without my having to worry about blocking it). Otherwise, people who know a lot less than me might never be able to figure-out what they've done wrong.
Bonjour is a great idea, and is built-in to Mac/iPhone: however, I can't spot any open-source implementation that I can use for other platforms. If any reader would be kind enough to point me to such an implementation, I'd love to take a look!