Jon,
It is hacky. I have done work with Bootstrap (with a colleague at a former company) and I've made Marketo behave pretty well with it. Feel free to look at my code here: http://go.servicetrade.com/DemoRequest.html (did some custom styling of error states as well. Can't leave well enough alone!)
Apparently "Forms 2.0" is coming out later this month and will offers some better form functionality, but I haven't seen it in practice.