Here's a patch for the issue with DATE objects, just mentioned [1]: https://gist.github.com/kaspersorensen/6319391
[1] Email thread "Date format to insert in salesforce": "In the salesforce module we always convert incoming Date values using a SimpleDateFormat with the UTC timezone. This is because SF saves the dates in UTC, so we have to ensure we don't wrongly send a date in the wrong format. All well. But a problem is that we also do this (apply timezone) for DATE columns, which are columns that don't have any time-of-day information (like a birthdate). In such scenarios we should not apply a timezone since it may change the actual date that we're submitting to SF. This is a bug which I'll post a patch for shortly."
