Trying to get a ton (600K) of JSON via XHR into IE.. silently failing. Oh, it fetches the data, it just can't parse the data, either through jQuery's built-in JSON parsing or even by the ol' eval.
Trimming the data down to 60K, there were no problems. The data is a repeating set of dummy objects, so I'm almost certain that I didn't just happen to trim out some problem section of the data. I'm convinced that IE is choking on the data simply because it is more than it can handle. My guess is that JScript doesn't throw the usual "your script is taking too long to execute" warning when executing a single "eval".
I 'solved' the problem by ditching XHR and using dynamic script tags: