If you're a FreeHand user and have recently been spending more of your time in Illustrator, you've no doubt experienced the frustration of living in a new world. The Appendix in the Real World Illustrator CS2 book (written by James Talmage) can help. And so can this new resource from Adobe - The FreeHand to Illustrator Migration Guide.
The document has the usual marketing spin from Adobe, but has some great info in understanding some of the major differences between the two vector applications.
In addition, if you want some general information on Illustrator CS, A Guide to Discovering Adobe Illustrator CS2 can prove helpful as well.