At the moment, it'll show the correct background color, but won't show the gradient. That is, if you slide the "puffiness" slider all the way to the left, that's what the buttons will look like on IE. I'm hoping to get that IE filter in there this afternoon. Will update here once it's deployed.
Update: I've added in the "filter" line, so it should work in IE as well. I don't have a way to test it, though, so if any of you have IE running and can confirm that you do, in fact, see a gradient on the buttons, I'd appreciate it.
If it doesn't work for you, rather than posting here, e-mail me, at charlie@monotask.com. Thanks!