As mentioned earlier by Macworld, Witch’s magic window-specific app switching was broken by App Tamer’s CPU-saving ability to halt background applications, but the newly-released Witch 3.5.5 solves this problem. App Tamer is also receiving an upgrade to 1.0.1 shortly, which removes a warning about Witch’s incompatibility. Both updates also have minor maintenance and bug-fixing tweaks.
Both upgrades are free for registered users. App Tamer is $15 with a 15-day free trial; Witch is $19 with a free 250-switches trial. So far, I’ve been running both, using the Witch beta, without problems, which bodes well.