Grr. Okay, so here's the confession:
But one thing kept bugging the hell out of me: floats didn't work well. If at all. And now I know why.
A long time ago, for miscellaneous reasons of ideological purity, we decided to go with a Strict DTD in the DOCTYPE header over at Isilon. Our assignment was to code to IE7, Firefox 2, and Safari. It turns out that if you don't put one of those in the header, IE7 interprets some things in an IE6-ish fashion, including floats and margins.
How annoying. For the first time in my life, I actually have to learn what "Quirks Mode" means. Well, now I know.
The funny thing is, we never had to worry about this at Isilon. We'd set it once in the heirachy header, and that was that. That was all we needed. Even better, it was XHTML pure because we used a python-sided templating engine that made it impossible to write improperly closed HTML.
Live and learn. One more thing for the developer/designer checklist.