Recently I received a report that our RSS feed was down, throwing an XML error. Upon inspection, I could see that white space was being added to everything on the site. Since XML is notoriously picky about syntax, that's where the issue appeared most prominently.
After a process of elimination, I discovered that when I deactivate Tubepress the issue disappears. Activate it, and the issue returns.
I know there are ways to suppress white space on a WordPress install, but these methods tend to "touch" core files, so not really ideal.