In some steps of the survey, when I fill in a form and click "next", it jumps back to the first page.
This has happened three times now, every time at a different point: First on the third page (IIRC; been a long day), then a few pages later, then again a few pages later.
The choices I made on the page I was on before the reset happened are not saved; the previous changes are (which makes it annoying, but not impossible to finish the survey.)
This seems to have been reproduced by at least 2 users, one here in the comments and one in the blog entry.
Edit: It happened again, right before the finishing line. Devs: If you need debugging info, the E-Mail address I specified in the survey is pekka at gmx dot de - feel free to take a look. Also, I (sadly) have a static IP so finding me shouldn't be difficult.
Edit 2: I just realized this is a problem on SurveyMonkey's part and not on SO's. Still, I guess this is relevant for SO, so I'm leaving it open.