We had another few issues yesterday afternoon, but we think we've got the problem licked. Here's what we've done:

• our front end "primary" apache servers seem to be getting into a corrupted state. Why this is happening is a mystery to us, but mod_rewrite seems to be combining bits of different queries together, just giving the "cycling through pages" issue. We've "solved" this by frequently cycling these servers, which isn't a great solution but it's good enough for showbiz. We're tracking this deeper.
• we've improved our core query (essentially, find an entry with a set of tags, some of which are very common) by 50x. Even out-of-cache page loads now are sub-second, so we're very excited by this to say the least.
• we had a problem with Internet Explorer browsers and posting -- we've fixed this, and if you're still seeing a problem, trying reloading your page to get the latest JavaScript includes
• We've made a number of UTF-8/Unicode fixes, so you can now view (and potentially edit) pages that look like this.