If I browse podcasts in iTunes on my (iOS 5.1.1) iPhone 4, most listings of episodes don't even fully load, with the download buttons (or sometimes the entire listing) failing to render. The exact same podcasts on my wife's iPhone 4S on the same wifi network work perfectly.
There's almost 20 GB of space available in my iPhone, and I've tried ending all apps & rebooting the phone multiple times.