I posted before from the WordPress iPhone application when it was released. Its pretty nifty. When they upgraded it to 1.1 though I could no longer get it to work on my blog anymore. I was mighty confused since it worked for every other blog that is hosted on my server, but not mine.
I finally did some digging into the problem and for some reason my blog wasn't outputting an RSD link which is needed for the application to find the XML-RPC endpoint. A quick
grep -R rsd found the issue.
That was hiding out in my functions.php file. I removed it and I'm cooking along with the iPhone WordPress application again. Beware if your theme does something similar. Found and fixed just before leaving town!