Tree Sap
Use rubbing alcohol, kerosene, WD40, TW Bug & Tar remover on a cotton ball. Used lightly these should not damage paint. You must apply these chemicals very lightly to avoid damage to paint.
Nail polish remover (acetone) is not recommended -- it leaves marks that polishing does not remove easily.
Also see: http://www.bmwworld.com/repairs/detailing/tree_sap.htm
Source: http://www.mr2oc.com/showthread.php?t=121371, http://www.mr2oc.com/showthread.php?t=29645
