[Scorponok]

What, so you spoof your client so you can get a version that's unusable in your browser because of its poor feature support? That doesn't sound like a great idea.

[wizzard]

If you're desperate for new features, you might not care if the CSS is a little wonky.

[thedufer]

That's not a good idea, for the record. We dropped IE9 so that core features could drop IE9 support, not to save a little CSS work. In the near future Trello will become quite unstable in IE9.