It looks like I'm not the only one encountering those problems. Rather than power off/on, I usually ssh into it and either reboot or issue a 'killall plexhometheater'. To make that even easier I thought that maybe I could map the killall command to a key on my remote... would that be possible?
On another note, could the freezes be avoided by switching to a Model B2? I'm already on the newest version (188.8.131.52-573b6d73), so a software update won't help. Other than that, I'm very happy with it.