Looks like there is something tripping up the agent - you see that kind of a result when the agent crashes (usually when it is checking the optimizations). I opened a bug to track it and should be able to look at it and get it fixed in the next day or so. It’s not a problem with your site, in that case there would be test results but with an error displayed.
No good new anyway. The browser is hanging in the middle of loading the page and there are no useful call stacks pointing to any code so it’s going to be quite a bit more involved to track down.
No, I’m 90+% sure that something I’m doing is pissing off IE, it’s just not obvious exactly what. The old codebase (used for IE) is pretty crufty and has been patched over 5 years so I’m cautiously optimistic that it won’t be a problem on the new code (which is much cleaner and is used for all 3 browsers).
Do you have any field data from Google Analytics site speed or something else? There’s a good chance that there’s a timing-sensitive issue with the async ads that is really pushing out the onload, particularly since it doesn’t appear to happen 100% of the time: http://www.webpagetest.org/result/120326_92_3QMKZ/
Sorry, not yet - things have been kind of crazy and it’s not at the top of my priority list so it got pushed back. I’m hoping to work on the Chrome timeline data this week but IE will be at least a week or two out before I get to look at it again.