Anyway, so I didn't think too much of that. Until today, when I had the pleasure of "porting" some code to work in IE8. To be fair, this app hasn't been tested much on IE period, before today. So, here's me dutifully reporting my findings.
<meta http-equiv="X-UA-Compatible" content="IE=7" />
Second, make sure you specify the doctype. We used html 4.01 strict. If you don't specify it, standard things like transparencies won't work. This should be obvious.
One more thing that was interesting was that forgetting to write var in front of a new variable caused an error to be throw. That looks a lot like strict mode behavior. I'll have to take a second look at this to verify, but it is worth mentioning.
Oh, almost forgot: on the positive side, MS did a great job with the built-in developer tool, which opens in a separate window via F12. I used it to inspect the DOM and change css attributes on the fly. I am sure it can do more that I haven't tried. Kudos to the IE team for that.