As I mentioned last Wednesday, turning on iTunes Match on my iPhone turned off the ability to create my own custom playlists for podcasts. In the short term I used SpeedUp since it supports creating your own playlists from any item in your music library, but two annoyances remained: First, I had to manually mark as read all the episodes I listened to, and I still remained dependent on syncing with my iTunes library to get the latest episodes before going to work in the morning. While Wi-Fi synching alleviated the whole process, I still had each day to maintain my playlist.
So I'm going back to using Instacast on the iPhone to manage and download my podcasts. It has a decent UI, supports password-protected podcasts, auto-cleans read episodes from the phone's storage, and so on. It doesn't support user-made playlists, but you can continuously play all episodes of all podcasts in ascending chronological order, so for me that's good enough. The only other downside I can think of is that it's a bit expensive, and the iPad version is not worth it. Video podcasts will remain on my "media center" Mac mini, but for audio podcasts I now have a hassle-free solution.