There was some general confusion around Marketo's support for IE (specifically, older versions of IE).
Though we have stopped supporting IE8 and lower within the Marketo application UI, we still support these browsers for all assets you are exposing to your customers.
Your forms should work on older versions of IE as well. If you have an issue with forms on any version of IE, please make sure to log a support ticket.
There are some minor "look and feel" issues that we've decided to let be in some older browsers, but if you feel something is awry, definitely send a report.
We've re-emphasized that IE support is a must for Forms 2.0 with the Support team.
Apologies for any confusion / slowdown that might have been caused by this confusion. We are definitely working to iron out kinks with IE support.